HAZOP Worksheet TemplateProject: 3 Phase SeparatorDate: 27/4

P&ID No.: 0001Node No.: G-05-100

Node Description: 3 Phase Separator Gas Outlet Line

HAZOP Lead: Thien Yee KiongHAZOP Scribe: Kelvin Tan

Table of Contents1.0 Introduction42.0 Process Description42.1 Assumptions52.2 Process Design and Methodology53.0 Operational Design133.1 Control System Design133.2 Operating Procedures163.3 HAZID STUDY (S&T HEAT EXCHANGER)184.0 Mechanical Engineering Design204.1 Mechanical Drawing25Part B271.0 Introduction (Flash Vessel)271.1 Scope of work272.0 Process Design272.1 Design methodology272.2 Basic Design Data282.3 Process design calculation283.0 Operational Design303.2Operating procedure31Operational check out list procedure [6]313.3 Safety Study (HAZID)344.0 Mechanical design384.1 Mechanical Drawing455.0Critical Review46Flash Tank46Heat Exchanger46References47

List of Figure Figure 1 P&ID diagram for shell and tube heat exchanger15Figure 2 Torrispherical head [10]21Figure 3 Mechanical design of heat exchanger25Figure 4 Piping and Instrumentation diagram for flash tank30Figure 5 Stresses in a cylindrical shell under combined loading [3]39Figure 6 Principal stresses on up-wind side [3]41Figure 7 Typical straight skirt support design [3]43Figure 8 Flange ring dimensions [3]44Figure 9 Standard bolt size M24 and dimensions [3]44Figure 10 Flash tank mechanical design45

List of Table Table 1 Stream table for the inlet and out stream of process fluid in HX-1023Table 2 Iteration summary of condensing coefficient8Table 3: Iteration process for converging overall heat transfer coefficient10Table 4 Design Outcome12Table 5 Component of control system and its function in heat exchanger P&ID (figure 1)13Table 6 Slurry spill accident respond 16Table 7 S&T Heat exchanger hazid study17Table 8 Standard skirt dimension24Table 9 Heat exchanger specification sheet 25

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1.0 Introduction Heat exchanger is selected as part of the major design with the purpose of heating up the spent liquor recycled from the precipitation process downstream in the alumina refinery plant. The active caustic soda content of the spent liquor, which intended to be recycled into digester for bauxite digestion, must be raised to a temperature higher than that required in bauxite digestion so as to prevent the interruption of physical and chemical conditions of the attack medium. This is mainly because usual bauxite temperature being fed into digester is insufficient and the temperature of the attack liquor must be raised from 120oC to about 156oC in order to obtain a temperature of 145oC in the liquor for bauxite digestion. Theoretically, the spent liquor recycled from precipitation process will circulate through a series of heaters and to be heated up from 80oC to roughly 120oC by heat exchanging with vapor from the flash tank evaporator. However, the main focus of the design is to achieve the outlet temperature of 110.8oC as simulated in SYSCAD at the last heater which feed with vapor from first flash tank in the alumina refinery plant [4]. The process parameter to achieve the design requirement is provided below where the data is extracted from SYSCAD. Table 1 Stream table for the inlet and out stream of process fluid in HX-102ParameterS021S041S040S042

Vapor fraction1.000.000.000.00

Liquid fraction0.001.001.001.00

Mass flowrate (kg/s)13.1713.171049.541049.54

Pressure (kPa)263.54263.54101.33101.33

Temperature (oC)138.26129.16103.26110.8

Heat duty ( kJ/h)6.27E87.32E83.77E101.52E9

Power (kW)-174282.07-203207.80-10430543.50-10459469.30

1.1 Objective of the design To design an effective heat exchanger with the determination for heat transfer area required from the given heat duty and temperature difference between hot and cold stream. Determination of pressure drop at the tube side of the heat exchanger and to achieve the shell side pressure drop as in SYSCAD model. Work out operational design which comprises of implementation of control system, operation procedures and as well as HAZID and HAZOP study. Work out the dimension required for the heat exchanger and as well as mechanical design.2.0 Process Description The heat exchanger will use energy from vapor hot stream discharged from flash tank to heat up the process cold stream. The hot inlet stream of the heat exchanger is purely vapor phase with mass flow rate and temperature of 13.17kg/s and 138.26 oC and exit at temperature of 129.16 oC. For the cold stream, spent liquor enter the heater at a flow rate of 1049.54 kg/s and temperature of 103.26 oC and exit at temperature 110.8oC and 303.3oC. From the data provided above, the only data that is not reliable is pressure for the process cold stream (S040 & S042). The SYSCAD model calculated it as atmospheric pressure as in steady state SYSCAD model, it does not take into consideration of pressure drop calculation neither in pipeline nor in shell side or tube side heat exchanger pressure drop. However, the inlet pressure for vapor stream is dependable as SYSCAD able to calculate the flash tank pressure through VLE equilibrium calculation. It is also the pressure which target to achieve at the shell side of heat exchanger. 2.1 Assumptions 1. Assume the pressure drop calculated by Kerns method at the tube side is reliable and accurate. 2. Ignore the non-condensable air in heat exchanger for ease of calculation. This is because in actual case air might be dissolve in slurry liquid which pose the issue need to vent non- condensable air in heat exchanger. 3. Total condensation is used in heat exchanger for the ease of calculation as only condensed liquid is consider in heat exchanger. 2.2 Process Design and Methodology In the heat exchanger design, Kerns method is selected due to its simple calculation method in providing satisfactory heat transfer coefficient for standard design. The method developed was based on experimental data for commercial heat exchangers and the data obtained were correlated by simple equation analogous to equation of flow in tube. However, the drawback of the design method is that it does not adequately account for baffle to shell and tube to baffle leakages and as well as bypassing. Hence, the pressure drop estimated through the method is less satisfactory compared to Bell or Delaware method [3].1. Heat Exchanger Selection [2,3]Shell and tube heat exchanger is chosen mainly due to the reason that it consists of large heating area per unit volume and thus high heat transfer rate in a clean condition. Lower capital cost will be resulted in comparison to that before the provision of sparing is taken into consideration for maintenance and cleaning. In addition, it is a off the shelf solution with many suppliers and world renowned technology. On the other hand, in high temperature application usually with temperature above 140oC, it has the disadvantages of high tendency for tube blockages, high scaling issues which make the cleaning and maintenance difficult. Hence, split ring floating head is selected for the purposes of ease of cleaning where defective tube can be replaced or plugged easily, shell side cleaning is favorable at infrequent interval, much less bypass area as more tube per shell diameter can be accommodated than the pull through floating head bundle. Moreover, it is more flexible with large temperature differential where it is good in startup or emergency condition since thermal stress at operating level is low (low ) in the process design. As the stream 41 liquid fractions is 1.0 as shown in table 1 and purely water, it indicates that the vapor undergoes condensation in heat exchanger and thus shell and tube condenser design should be considered. 2. Fluid Allocation [2,3]Series of factors like corrosion, fouling and cleaning considerations have been accounted. Highly corrosive spent liquor mainly due to its active content of caustic soda is assigned to be placed in the tubes where the corroded tubes can be replaced easily. Moreover, cost also can be saved on material construction on the shell side where the body of the shell needs not to be made of corrosive-resistance material. As process fluid will foul the tube, it is vital to control the process fluid in tube to be in the range of 1-3m/s so that to reduce scaling and obtain reasonable maintenance frequency. Therefore, spent liquor is to be allocated in the tube side of heat exchanger. On the other hand, shell side condensation of vapor is preferable due to the reasons stated before. Detailed Design Calculation In the design, horizontal baffled shell and tube condenser is employed as the design is good for single component vapor, relatively high and low pressure drop design, and liquid coolant. It is to note that in actual case it is not a coolant as spent liquor is to be heated up. The shell side condensation calculation for pressure drop and heat transfer coefficient calculation method will be following what have been proposing for calculation in a typical condenser design which takes into consideration of condensing vapor outside the tube while single phase flow calculation will be accounted for pressure drop and heat transfer coefficient calculation in tube for spent liquor. 3. Heat duty (heat transfer rate) [3]As the primary objective of the design is to work out heat transfer area required and the prerequisite of it is to determine the heat transfer rate per unit time for vapor stream as equation follows: Heat transferred from vaporq =

= 13.17 (2738.87 542.74) = 28923.03 kW

4. Overall heat transfer coefficient [3]Overall heat transfer coefficient is the reciprocal of the overall resistance to heat transfer and as the first trial it is determined to be as 2000 W/m2oC. HATCH provided the value of overall heat transfer coefficient to be 1200W/m2oC in partially scaled condition and high heat transfer coefficient is favorable as it is proportional to heat transfer rate. Thus, it is assumed that in clean tube condition; the Uo(ass) is 2000W/m2oC.

5. Mean temperature difference [3]As temperature difference between both the process cold and hot stream change along with length of heat exchanger, logarithmic Mean Temperature Difference LMTD (a form of driving force which is equivalent to average temperature different) is used to determine the heat transfer rate. Counter current flow is used in the tube and shell design as it provides greater LMTD than co-current flow. Thus, grater heat transfer can be achieved under same surface area [1]. As the condensation range is small and the variation in saturation temperature will be linear, the logarithmic mean temperature different is suitable for the design.

Then the logarithmic mean temperature can be calculated:

By first guessing two tube passes for a horizontal heat exchanger, condensation in one shell; true temperature difference can then be determined through the value calculated above:

6. Heat transfer area [3]The trial heat transfer area is calculated as follows:

7. Selection of tube dimension [3]The tube dimension is selected based on tube cleaning practices as minimum limit of the outer diameter is approximately 20mm. By taking the tube dimension as 22.225 mm outer diameter with 19.736 mm inner diameter as recommended by handbook the surface area of one tube is calculated as below [2]: As = OD x x L= 22.225 x 3.142 x 7.32= 0.51 m2

The tube length 7.32m is selected based on the criteria that high cost can be avoided with long tube used. Moreover, the tube length is chosen with the consideration that length to shell diameter ratio must be in the range of 5 to 10 for best performance.

8. Number of tubes [3] Number of tubes is computed through the formula of N = = = 1516.23

9. Tube Layout [3]Triangular pitch is chosen as the configuration is compact and provides higher heat transfer. The formula for tube pitch is as follows: Pt = 1.25do = 1.25x 22.225 = 27.78

With calculated number of tubes and selected tube OD, shell bundle diameter can easily be found through equation of,http://www.hcheattransfer.com/shell_and_tube.html = Where the constant K1 and N1 are determined from table 12.4 in [3], with the configuration of 2 tube passes and triangular pitch selected.

Number of tube in centre row which is also the row at the shell equator is calculated by: Nr = = = 41.4810. Shell-Side Coefficient [3]As vapor is condensing outside the wall of tube, hence tube wall temperature, Tw is required to be determined through mean temperature at the shell side and tube side. By assuming condensing coefficient of 1500 W/m2oC at the shell side, the equations for mean temperature and wall temperature are given by:Mean temperature Shell side = = =133.71Tube side = = = 107.03Tube Wall Temperature (TMS Tw) x = (TMS TMT) x Uo(133.71 Tw) x 1500 = (133.71 107.03) x 2000Tw = 98.14 oC

Mean Temperature Condensate = = 115.93oCPhysical properties at 115.93 oC for condensate = 0.000241 Ns/m2 = 946.48 kg/m3 = 0.68 W/mKVapor density at mean vapor temperature = 1.425 kg/m3 = = 0.0012 kg/smAverage number of tube in vertical tube row, typically of the number in the central row is used:Nrv = x Nr = x 41.48 = 27.6511. Mean coefficient for a tube bundle [3] The equation below accounts for condensation of vapor on the outer horizontal tube and as well as flow of condensate from row to row over the Nr tubes in a vertical row. Moreover, it also taking into consideration of the obstacle flow of condensate around the tube as condensate is impossible to flow smoothly from row to row of tubes in reality. (hc)b = 0.95kL ( )1/3 = 0.95 x 0.68 ()1/3 x 27.65-1/6 = 11677.47W/m2oC The calculated condensing coefficient 11677.47 W/m2oC is far apart from the assumed value of 1500 W/m2oC, hence correction to Tw is needed and iteration is required to be carried out. Table 2 provided the summary of iteration and converged value of condensing coefficient.Table 2 Iteration summary of condensing coefficientParametersBase case1st Iteration2st Iteration

Shell side mean temperature (oC)133.71133.71133.71

Tube side mean temperature (oC)107.03107.03107.03

Tube wall temperature, Tw (oC)98.14129.14129.28

Condensate mean temperature (oC)115.92131.43131.50

Mean condensing coefficient for tube bundle, (hc)b (W/m2oC)1500.0012055.92

12055.92(converged)

12. Tube side coefficient [3]Tube cross sectional area, TCSA = x = x = 0.23 m2Density of spent liquor at 107.03oC = 1247.28 kg/m3Tube velocity = = = 3.63 m/sPrandtle number which define ratio of momentum diffusivity to thermal diffusivity and Reynolds numbers that determine type of fluids flow inside the tubes are given by:Pr = = = 9.45Re = = = 182248.40As the calculated Re>2100 and it showed the characteristic of turbulent flow, the heat transfer coefficient at the tube side can be determined by: hi = 0.023 =0.023 = 7516.06 w/moC13. Overall Heat Transfer Coefficient [3]Nickel alloy 400 is selected as the tube material and with a conductivity of, kw of 24. 54 W/m2C and fouling coefficient of steam condensate and aqueous salt solution are assumed to be 5000W/m2oC respectively 0 which is at the maximum of the range of fouling factor coefficient 5000W/m2oC respectively so as to maximize the Uo; the overall heat transfer coefficient is calculated by the equation of

The overall heat transfer coefficient is calculated as W/m2C which is far from the estimated Uo of 2000 W/m2C. Iterations have to be conducted to get the converged Uo value. Table below provided the summary of iterated data with the use of 1404.92 W/m2oC as the trial coefficient for repeated steps calculations.Table 3: Iteration process for converging overall heat transfer coefficientParametersBase Case1st Iteration2st Iteration

Uo(ass)20001404.921369.57

Area775.041103.321131.80

Tube velocity3.632.551.79

Bundle diameter 1.151.351.37

Shell side coefficient12055.9213562.0513677.76

Tube side coefficient7516.065666.165666.16

Overall heat coefficient, Uo1404.921369.571369.57

14. Shell side pressure drop [3]As floating head split ring is employed, the clearance for the diameter bundle of 1.37m as provided from the figure 12.10 in [3] is 69mm. Baffle spacing for condenser has to be minimum of 35% of shell diameter to prevent excessive bypassing and leakage. Thus, 42% of the baffle spacing is selected to provide high heat transfer rate and achieve reasonable high pressure drop across the shell of the heat exchanger as required by SYSCAD. As the design is with total condensation assumption, cross flow design of shell is vital to be used. It has a partially filled shell with space above the bundle to distribute the vapors along the entire length. Hence, cross flow area is important to be considered and can be calculated with equation of

The shell side mass velocity can be calculated as follows:

The equivalent diameter is computed by using the equation for triangle pitch arrangement:

With vapour viscosity of 0.0000135 Ns/m2 at mean vapor temperature (133.71oC), the shell side Reynolds number can then be calculated:

From the Figure 12.30 in [3] with Reynoldss number of, the friction factor, is obtain to be 0.029, then the linear velocity can be determined by:

The shell side pressure drop, is determined by and viscosity factor is neglected:

As pressure drop on the condensing side is difficult to be predicted due to the existence of two phases and vapor mass velocity is varying throughout the condenser. For total condensation, Kerns suggested a factor of 50% of calculated pressure drop using inlet flow where it takes into account for the change in vapor velocity using method of single phase flow.

15. Tube side pressure drop [3]The viscosity of caustic soda at is , and the Reynolds number can be calculated:

Friction factor, is obtain to be 0.0028 from table 12.24 (Sinnott 2003). By neglecting viscosity correction, the tube side pressure drop can be calculated as:

Table 4 Design OutcomeOverall HX-102 design summary

Tube outer diameter, mm22.225

Tube inner diameter, mm19.735

Tube length, m 7.34

Tube velocity m/s2.56

Shell velocity m/s26.66

Triangular pitch, m27.78

Shell Diameter, mm1435.07

Baffle spacing, mm602.73

Baffle cut, %42

Overall Heat Transfer Coefficient, U, W/m2K1370.56

Pressure drop in tube, kPa43.61

Pressure drop in shell, kPa259.46

Comment: The overall design is satisfactory. This is because of reasonable tube side velocity which falls in the range of 1-3m/s. Shell side average vapor velocity is 26.66m/s, which is reasonable as the shell side vapor velocity fall in the range of 10 -30 m/s. The 26.6m/s is actually taking the mean velocity at inlet vapor stream which is 56.24m/s and velocity at outlet condensate stream 0.08m/s The pressure drop in shell is nearest to the value of 263.54kPa as shown in SYSCAD. The obtained shell side pressure is particularly designed to be lower than the pressure stated in SYSCAD to ensure the vapor flow from high pressure flash tank to low pressure without reverse flow. The pressure drop in tube side is also make sense as usually in series of heat exchanger the HX-105 will have the highest tube side pressure drop (300kPa from HATCH) and pump need to ensure the spent liquid have enough energy to flow towards all the 5 heat exchangers. The pressure should be of from high to low. And the tube side pressure drop is valid with 43.61kpa < than 300 kPa. 3.0 Operational Design 3.1 Control System DesignControl system have the advantages of correcting the effects of disturbances in feed flow rate, temperature, steam supply pressure and so on through various type of instrumentation control system. It can be feed forward, feedback, cascade or inferential control. Figure 1 showed the P&ID diagram for heat exchanger that would be sufficient in controlling the heat exchanger with the control system proposed.Main control objective is to transfer energy from hot vapor stream to cold spent liquor stream. The type of control proposed is cascade control loop. It consists of two controllers in series that working together in order to correct the disturbances incurred. In the diagram, the cascade master temperature indicator transmitter (TIT) detecting variation in temperature and the slave controller (PIT) will then detects the variable that affect the process temperature which is pressure of the steam. The cascade master (TIC) will then adjust the set point of slave controller (PIC) to attain the process system back to normal. It has the advantages of accounting for disturbances in primary variable (temperature for spend liquor in the case) quickly and effectively. In addition, the control system also helps to reduce the dead time and phase lag time in the system which is good for more efficient control of the process flow in the heat exchanger. The control system is important in the sense of too much or too less heat transfer from vapor might lead to the target to achieve 110.8oC at the spent liquor outlet stream impossible. And this will upset the performance of digestion of bauxite in digester if required temperature is not achieve or too high. High heat differential transfer will lead to thermal expansion of the heat exchanger and as well as speed up the scaling of liquor on the tube side of heat exchanger or tube rupture might be result. Thus, control system is imperative to be installed in heat exchanger for best performance [11].Table 5 Component of control system and its function in heat exchanger P&ID (figure 1)No

1Vapor Inlet S-021

ComponentsFunction

Check valve V-10To prevent reverse flow of vapor

Gate valve V-25To bypass and act as a backup valve

Isolation valve V-3,V-2To isolate V-01 for maintenance purposes

2Shell and Tube Heat Exchanger HX-102

ComponentsFunction

Vent V-16For maintenance purposes and to vent non- condensable air

Pressure safety valve V-69Protection valve that prevent the tube rupture due to extreme pressure fluctuation

Drain V-26To drain condensate for maintenance purposes

3Water (Condensate) Outlet S-041

ComponentsFunction

Isolation valve V-66, V-67To isolate V-65 for maintenance purposes

Gate valve V-68To bypass and act as a backup valve

Check valve V-42To prevent reverse flow of water

Flanged valve with spectacle blind V-65To stop/ block the fluid from flowing into heat exchanger or flowing out

4Spent Liquor Inlet S-040

ComponentsFunction

Isolation valve V-38, V-39To isolate V-01 for maintenance purposes

Gate valves V-40To bypass and act as a backup valve

Check valve V-34To prevent reverse flow of liquor

Flanged valve with spectacle blind V-35To stop/ block the fluid flow into heat exchanger or flowing out

Drain valve V-37To drain spent liquor for maintenance purposes

5Spent Liquor Outlet S-042

ComponentsFunction

Flanged valve with spectacle blind V-72To stop/ block the fluid from flowing into heat exchanger or flowing out

Gate valve V-75To bypass and act as a backup valve

Isolation valve V-73, V-74To isolate V-72 for maintenance purposes

Check valve V-62To prevent reverse flow of spent liquor

Drain valve V-61To drain spent liquor for maintenance purposes

6Control System

ComponentsFunction

Temperature indicator controller TICReceive signal from TIT which first compare the variation of set point and perform action on PIC

Temperature indicator transmitter TITDetect temperature variation from set point and send signal to TIC

Pressure indicator controller PICPerform action on control valve to adjust the pressure of vapor

Pressure indicator transmitter PITDetect variation of pressure from set point and transmit signal to PIC

High pressure alarm HTo notify when pressure is high

Low pressure alarm LTo notify when pressure is low

Figure 1 P&ID diagram for shell and tube heat exchanger

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3.2 Operating ProceduresCommissioning [9]Before commencing a heat exchanger into operation, it is advisable that reference should be made to the heat exchanger specification sheet, drawing and as well as name plate for any special instructions. This is to ensure the heat exchanger will never be operated under condition that exceeds those specified on the specification sheet for safety purposes. Moreover, local safety health and regulations should be considered. Incorrect way of startup or shutdown steps would cause leaking of bolted flanged joints and tube to tube sheet joint. Start up operation [9]The process fluids must be introduced into the shell and tube heat exchanger in a way that minimized the differential thermal expansion between the shell and tubes. Cold process stream should first be flowing into heat exchanger and only followed by gradual introduction of hotter medium like vapor. During the start up, the vent valves should be unlock and left opened until all the passages have been purged of air and completely filled with fluid.Shutdown operation [9]Gradually stopping the flow of hotter medium then only followed by colder medium in the equipment. The aim for gradual shut down is to minimized differential thermal expansion between the shell and tubes. After completely shut down, all components of the equipment and as well as pipeline should be drained completely in order to prevent the freezing or corrosion from happening in the equipment. Water hammer is unfavorable in pipeline as it will incur multiphase flow and it is advisable that condensate be drained from the heater during start up or shut down. Tube side of exchanger can be blown out with air ti reduce water retention in the equipment. Maintenance [9]For daily checking procedure, it is vital to check for any process fluid leaks in the sealed area of the heat exchanger.Periodical maintenance [9]Keep eyes on corrosion or fouling in the pipeline or heat exchanger by performing periodic cleaning to the equipment. Check for visible cracks, for any of the equipments component, integrity of liners and etc. Disassembly [9]All pipings must be sealed/ disconnected prior to disassembly.Check for internal pressure of the heat exchanger after the hydraulic pump is halt for operation and make sure the pressure is zero before disassembling the heat exchanger,It is also vital for users to check that the equipment is fully depressurized, vented, drained, neutralized or drained before disassemble the heat exchanger.Keep all the log books that record down the event or operation malfunction which affect the heat exchanger performance. This is to ensure no repeatable mistake in operation in the future. Environmental accident response procedure The most corrosive fluid in heat exchanger is caustic soda and immediate action should be taken if leakages are found. As the caustic soda is highly corrosive in nature, it would bring harm to human and environment if cares is not taken immediately.Table 6 Slurry spill accident respond [8]CategorySizeResponseTreatment Materials

Smallup to 300ccAbsorption or chemical treatmentCaustic neutralizer orabsorption material like sand or socks

Medium300 cc - 5 litersAbsorptionAbsorption materials

Largemore than 5 litersPublic safety must be calledoutside help

1.1. Determine the size of spill/ leakage and take appropriate action according to the table proposed below.1.2. Contain and clean up the leaks with the chemical used.

Emergency shutdown procedure [9]For safety control, pressure relief valve and emergency shutdown valve are being installed into the equipment. If pressure in the heat exchanger went abnormal, the set pressure in the pressure relief valve will be activated and hence relieving the emergency situation. However, if PRV malfunction, emergency shutdown valve will be activated when it detects 20% extra high temperature in the stream and alarm will ring and fluid flow will be shut down immediately.

3.3 HAZID STUDY (S&T HEAT EXCHANGER)Table 7 S&T Heat exchanger hazid study HAZARDIDHAZARD CATEGORY (GUIDEWORD)HAZARD DESCRIPTION / HAZARDOUS EVENT

CONSEQUENCESPREVENTION / DETECTION / BARRIESRISK ASSESSMENTRECOMMENDATIONSACTIONS

LIKELIHOODCONSEQUENCESEVERITYRANKING

1

Natural DisastersExtreme heatPressure build up in HX-102

Heat stress of personnel

Pipeline an equipment thermal expansion

HX-102 operate higher than operating temperature of 80CShut down operation

Evacuate personnel from extreme heat

PossibleLowLowMonitor the operating temperature of HX-102

Install high temperature alarm on HX-102Operators to do temperature monitoring

Electrical engineering team to install alarms

Operators to inspect the equipment and pipeline condition.

2

External EffectsDropped objectsDamage of HX-102

Possible rupture of HX-102, thus release of corrosive caustic

Injury or death of the workers Inspect regularly for overhead equipment and possible loose items.

UnlikelyCriticalExtremeEnsure rigging is in good condition and operated correctly

Installation of safety netting above HX-102

Wearing protective hard hat and as well as personal protective equipmentsOffshore health and safety executive to handle all the safety requirement rule and regulations.

3

External EffectsFatigue/ cracking Rupture of pipeline

Loss of containment

Cracking of HX-102 shell

Loss of alumina productionN/AUnlikelyMajorHighPerform non destructive testing (NDT) on vessel to test vessel thickness and pipeline integrity

Visual inspection of any hairline crack on the equipment.

Maintenance engineering team to perform the testing and fix broken pipeline or equipment leakage.

4

Human FactorsImproper/inadequate trainingLoss of production

Process upset and abnormal operating condition

Damage to equipment which might include HX-102

Explosion N/A PossibleCriticalExtremeProvide adequate training for operators

Compulsory in preparing operating procedure manual by designers and the procedure have to be strictly obeyed

Designers/ consultants to provide the training.

Operators to obey the rule and regulations from the operating manual

5

Equipment/Instrumentation Malfunction

Control valve V-01 failureNo heat exchange (fail to open)

HX-102 over pressurized (fail to close)

Loss of containment (fail to close)N/AUnlikelyMajorHighInstall bypass valve to the control valve

Install isolation valves around valve V-01 for maintenance of broken V-01Process engineering team to design and maintenance team to install bypass and isolation valves

6Process UpsetsFlow deviation Increase in temperature in HX-102 Insufficient temperature to digest bauxite oreN/ALikelyModerateHighInstallation of flow control system at the outlet stream of spent liquorProcess engineering team to design and electrician to install the control system

7

Process UpsetsPressure deviation HX-102 over pressurized and rupture

Loss of containment

Upsets to downstream equipment

Personal injury or deathRelief valve

Cascade controller system loop

Vent line V-16PossibleCriticalExtremeInstallation of emergency shutdown valve and high temperature alarm.

Electrical engineering team to install emergency shutdown valve connected to high temperature alarm and display at the indicator

8

Process UpsetsCorrosion/ erosion Cracking and leakage of HX-102 and as well as inlet and outlet pipelines S021, S040, S041, S042

Cracking of vessel or pipelineNickel alloy steel materials for all the pipelines and tube side of HX-102LikelyMajorExtremeVisual inspection on the pipeline for any possible defects.

Frequent non destructive test for pipeline and vessel wall thickness Operators to perform the checking periodically.

Maintenance engineering team to perform the testing.

9Utilities FailuresLoss of powerLoss of functionality of cascade control systems

Pressure build up in HX-102

Loss of alumina productionFail open/closed valves UnlikelyModerateModerateBackup generator for important process equipmentElectrical engineering team to install backup generator

4.0 Mechanical Engineering DesignThe mechanical design of shell and tube heat exchanger will be carried out based on process design data obtained. Shell side of heat exchanger will be designed as thin walled pressure vessel under the exertions of internal pressure. With the determined information given in table 4 summary of designed mechanical components are listed as follows:1. Pressure vessel arrangement and type of domed head and end closure.2. Wall thickness required for cylindrical vessel, shell cover, channel covers and tubesheet thickness3. Dead weight of vessel4. Elastic stability check5. Flanges6. Nozzles7. Gaskets8. Stress calculations9. Saddle support

Process and mechanical design information Shell and tube side passes: 1 shell 2 tube passesTubes number, layout size and type: 2206.54; tube length: 7.34m; tube OD: 22.225mm; ID: 19.736mm; equilateral triangular pitch; floating tube sheetShell diameter and head: Shell ID: 1435.07mm; torispherical head and carbon steel for shell and head. Corrosion allowance: 3mm of corrosion allowance is taken for carbon steel Design temperature and pressure: For safety design purposes, 10% extra of the design value will be taken into account. For temperature, the highest process fluid temperature is selected while highest inlet pressure among both the inlet stream is chosen. Design temperature: 1.1 x 138.26 = 47.97oC; pressure: 43.61 x 1.1 = 47.97kPaPermissible stress: 114.58 N/mm2 for carbon steel Shell diameter and thickness [3]Cylindrical shell is chosen as the shape for the heat exchanger and the minimum shell thickness can be calculated from the formula below which based in the maximum allowable stress and corrected joint efficiency:

= 3.71mmThe joint efficiency is taken as 0.85 with spot radiography and double welded butt joint. The low joint factor will give reasonably low cost and as well as compromise with thicker and heavier the vessel it will result. The minimum thickness for the cylindrical shell before the corrosion allowance is 3.41mm and the resulting thickness after the corrosion allowance is 3.71mm.

Arrangement of pressure vessel and type of domed head and end closure [12]As determined from the chart in .the design of heater is favorable of horizontal oriented pressure vessels. Torispherical head is chosen due to its common usage in chemical industries and suitable for high operating pressure which up to 200 psi.

Figure 2 Torrispherical head [10]The minimum thickness of a torrispherical head (th) can be determined by:th = + c= 3.54mmW = (3 + ) = 1.54 The channel cover thickness is calculated from the formula of

= 4.71mmVessel Dead Weight Load [12]With carbon steel cylindrical vessel and doomed ends, the estimated vessel weight isWV = 240CVDm(HV+0.8Dm)t =11.74kNWeight of tube plates:Plate area = 1.62 m2Weight of a plate = 1.2 X plate area = 1.2 x 1.62 = 1.94 kNNo. of tube plates = 1Weight of total number of plates = 1.94 kNTube sheet thickness [12]Tube sheet is fixed with shell and channel to form barrier for the process fluids in shell and tube side. It is a circular flat plate with drilled holes in regular pattern which might varies for every tube sheet layouts. Open end of tubes are connected to the tube sheet and usually the tube sheets are attached by welding or bolting or combination of both. The minimum tube sheet thickness which according to TEMA standard to resist bending is calculated through: = 14.17mm

Where F is taken as 1 for floating type tube sheet and mean ligament efficiency k is computed byk = 1 =0.43

Impingement plates requirement [12]It is usually installed on the tube side of a bundle which serves to slow down and disperse the fluid as it enters the exchanger. It helps in prolongs the lifespan of the tubes and as well as the bundle. The requirement for the installation of impingement plate is given by: than 1 m it is recommended to have nozzle ID of 0.254 m Gaskets [12]Gasket is designed in the way to make the metal to metal surfaces leak proof. The deformation of gaskets under load seals the surface irregularities between metal to metal surfaces which prevents leakage of the fluid. To prevent the leakage of the internal fluid, the residual gasket force must be larger than calculated force or required. The equation is presented below for the scenario mentioned: = = 1.0065Where DIG = Ds + 0.25 The gasket factor m is taken as 3 for corrugated metal with asbestos fill from the table of stated in [12] due to its ability to withstand in high temperature whereas Y is stated to be 3.87 for maximum design seating stress with the reference of gasket factor. From the calculated value of 1.0065 and DIG of 1.432m the gasket width can then be determined with formula ofGasket width, N = = 4.66mm Take 10 mm as the design for standard widthBolt design [12]The minimum initial bolt load at atmospheric pressure and temperature is given byWm1 = bGY =192043.3 NThe gasket is compressed under tight pressure and the required bolt load Wm2 is given byWm2 = H + Hp = 2bGmp + p = 79590.09NWhere G = mean gasket diameter, = 1.44mBasic gasket seating width bo = for flat flange, thus b0 = 10mm As calculated Wm1 is greater than Wm2Minimum bolt cross sectional area Am = = 21290.19 mm2M16 nominal thread diameter with bolt circle diameter (Cb) of 1470mm, 56 bolts and 22mm Dbr Are selected from https://law.resource.org/pub/in/bis/S08/is.4864-4870.1968.pdfMinimum gasket width, Nmin = = 1.00693Flange [12]For gasket seating condition (no internal load applied)W= = 358786.24N= = 5384521 NmmFlange force calculation (For operating condition)Hydrostatic end force for the inside area of flange, HD = = 77601.68NWhere B = outside shell diameter = 1435.07mmhD = = 17.465 mmMoment due to HD, MD = HDhD = 1355313 NmmGasket seating condition, HG = W H = 280652.1 NTaking W = Wm2Moment due to HG, MG = HGhG = 1455.959NhG = = 15.0076 mmMG = HGhG = 21850.45 NmmPressure force on the flange face, HT = H - HD = 532.45N hT = = 16.24mmMT = HThT = 8644.978 NmmSummation moments under operating condition, Mf = MD + MT +MG = 8644.98 NmmFrom the calculated value of 8644.98 Nmm it showed that is the controlling moment as it is greater than Mf.Flange thickness [12]Tf = = 55.14mmK = from graph; A is 1515 from chosen bolt while B= diameter of shell; hence K = 1.06mm; Y = 1.06

Saddle support [3]Horizontal heat exchanger is usually supported by at least two supporting saddle supports and assuming that the heat exchangers is uniformly laded, approximately 21 percent of the length of vessel will be placed at each end.

From the chart given in Figure 13.26 in [3], the dimension of the vessel is recommended according to the design is given as below:Table 8 Standard skirt dimensionVessel Dia.

Max. Weight

Dimensions (m)

mkNVYCE

1.21800.780.201.090.45

mmJG

t2t1Bolt dia.Bolt holes.0.360.14

12103430-

Although original design case is 1.45m, it is assumed that the support dimension can support the overall weight as extra details design is needed due to the reason that the data given by handbook is just limited to 12m. Moreover, the calculated weight is approximately 14 kN which is far way enough to support from the dimension above. The dimension data extracted from handbook is assumed to be applicable to heat exchanger design as more complex calculation is needed in order to work out the accurate data. 4.1 Mechanical Drawing

Figure 3 Mechanical design of heat exchanger

HE-101 Heat Exchanger Specification SheetEquipment No.HX-102

Sheet No.1

General Data

Functional Description To transfer heat from vapor in order to heat up spent liquor

Type of Heat ExchangerShell and tube, floating head type

OrientationHorizontal

OperationContinuous

Shell Side FluidVapor

Tube Side FluidSpent liquor

Operating Data

Total Heat Duty28923.03kW

Overall Heat Transfer Coefficient1369.57W/m2C

Heat Transfer Area1131.80m2

Performance of one Unit

Shell SideTube Side

FluidVaporSpent liquor

Mass Flow Rate13.171049.54kg/s

CompositionH2O (v)1.00H2O0.8886Mol fraction

Total NaOH0.0691

Other Comp. 0.0423

InletOutletInletOutlet

Temperature138.26129.16103.26110.80degC

Pressure (as in SYSCAD)263.54101.325kPa

Density1.431247.28kg/m3

Heat Capacity2.173.65kJ/kg.degC

Thermal Conductivity0.680.1898W/m.degC

Viscosity0.00001350.00049kg/ms

Construction of one Shell

Shell Inner Diameter1435.07mm

No. of Passes2 (Type F, TEMA Standards)

No. of Baffles3

Bundled Diameter1.37m

Total No. of Tubes2206

No. of Tubes per Pass2

Tube Outer Diameter22.225mm

Tube Inner Diameter19.736mm

Tube Length7.34mm

Pitch Diameter27.78mm(Triangular Pitch Arrangement)

Shell SideTube Side

Pressure Drop259.4643.61kPa

Material of ConstructionCarbon SteelNickel alloy 400

Prepared byKelvin Tan Khai YikDate: 7/11/2014

Checked byVincent Tan Kok YewDate: 7/11/2014

Table 9 Heat exchanger specification sheet (Critical review of heat exchanger is provided at part B of the report in section 5.0 which is combined together with flash tank due to space limit)

Part B1.0 Introduction (Flash Vessel)In alumina refinery plant, flash train vessels are commonly used equipments in digestion facility which aims to let down the pressure of the digester discharge slurry stream (S-019) into atmospheric pressure by mean to flash cool the slurry and to make the slurry concentrated. The high pressure slurry enters the low pressure flash tank FT-101 leads to the formation of liquid slurry and steam. In the flashing process, slurry will be cooled down through the evaporation of steam while the heat from the steam will be used in HX-102 for heating up the spent liquor. The flash tank design in the report is aimed to work out the required dimension of vessel in term of height and diameter to handle the amount of slurry feed to the vessel, position of the slurry entry nozzle, vapor outlet nozzle and as well as vessel arrangement. However, the constraint for the design is to ensure minimum slurry carry over with the outgoing vapor, sufficient hydraulic head for the transportation of fluid from tank to tank which need to compromise with the costing of elevation construction and wind loading. Sufficient hydraulic head to transport the slurry from tank to tank through the interconnecting flash piping is not enough as the pressure drop in pipeline might induce multiphase flow which will lead to erosion and pipeline wear [5]. 1.1 Scope of workProcess sizing of flash tank, operational design and as well as mechanical design are presented in the report. 2.0 Process Design The flash tank FT-101 is to flash cool incoming slurry from temperature of 145oC to 138.26oC. The operating condition in the flash tank is 263.54kPa. 2.1 Design methodologyTo ensure proper sizing and high performance of flash tank the design methodology is proposed as follows:0. Determination of terminal velocity and buoyancy0. Work out the condensate quality factor0. Conductivity of caustic calculation0. Diameter and height of flash vessel0. Preferred flash vessel tank orientation and inlet outlet entry

2.2 Basic Design DataParameterS019S020S021

Mass flowrate (kg/s)1212.151198.9813.17

Pressure (kPa)303.90263.54263.54

Density (kg/m3)1212.51277.781.42

Temperature (oC)145138.26138.26

Vapor Fraction001

Liquid Fraction0.960.960

Solid Fraction0.040.040

Heat Duty (kJ/h)3.76E103.7E106.3E8

Power (kW)-10439463.86-10265181.79-174282.07

Comment: The percentage of slurry flashes to vapor is 1.09% with the output of 13.17 kg/s of vapor at S021. Moreover, it can be seen from the stream table that the temperature of S019 is being reduced by 4.64% due to the thermal energy release with the vaporization of vapor. Thus, the process sizing of flash vessel have to take into the considerations that the objective of at least 4.64% temperature reduction, flow rate of slurry and vapor at the outlet and inlet can be achieved with the dimension and operating condition of flash tank designed.2.3 Process design calculationFlash tank sizing [HATCH]The buoyancy is taken into consideration of liquid buoyancy force that exert upward onto the vapor droplet. Hence, in order for vapor to flash, the vapor must have buoyancy force greater than gravitational force. The buoyancy equation is determined as follows: Buoyancy = = = 898.85 For vapor to flash without carrying over the liquid droplet, it is vital to calculate terminal velocity of vapor. The terminal velocity is the force balance on the liquid droplet and when the scenario of net gravity force balance the drag force happens, the heavier liquid will settle at constant terminal velocity. Thus, it is important to ensure that velocity of vapor is less than the terminal velocity to minimize the carryover of liquid by vapor and for the ease of heavier liquid settle out at the bottom of tank. The equation for terminal velocity is calculated by: Terminal velocity Ut = = 0.7It is given by HATCH as the guideline that the terminal velocity is 0.7. Condensate quality factor is to determine the purity of vapor flashed at the vapor outlet. It is vital to ensure that the vapor does not contaminate with slurry droplet as liquid carry over by vapor will reduce the heat exchanger performance at downstream and damage the equipment at shell side (prone to corrode due to alkaline medium). The equation is determine by:Condensate Quality Factork = = = 0.023The equation below presented the conductivity of caustic in the flash vessel. It is a vapor purity parameter to consider as high caustic content (characterize b high conductivity) will pose high chances in contaminating the vapor stream. The caustic concentration is obtained by SYSCAD with the value of 170 kg/m3.Target Conductivity = = = 147.65 The calculated 147.65 target conductivity is reasonable and showing the calculation is on the right track. This is because HATCH suggested the target conductivity value of < 200. Diameter With the determination of target conductivity and caustic concentration in flash tank, mass flow rate of vapor, the diameter of the flash vessel is then calculated by equation as follows: D = = = 4.14 m HeightThe determined diameter 4.14m is then substitute into equation below to determine the total height of flash tank. = 2.5H = 2.5 x 4.14 x 0.7 = 7.25 mHeight of slurry pool is 20% of total height of vessel= 0.2x 7.25=1.45m

3.0 Operational Design3.1 Control System The flash tank control system is basically made up of two control system. Pressure controller system will detect variation in vessel pressure and make adjustment to the valve to pressure relief it. For level control system, level indicator controller will detect variation in level and make adjustment to the control valve V-02. Low level alarm will ring when the level in the vessel is too low, action will be performed on V-11 to close the valve in order to wait for slurry build up in flash tank. Pressure relief valve is installed at the top of tank in case of emergency. Drainage valve V-15, V-13 and V-16 are provided for maintenance purposes. Isolation valves are installed on inlet and outlet stream of line to bypass the slurry when the control valve is malfunction. Refer to the diagram below for the control system.

Figure 4 Piping and Instrumentation diagram for flash tank

3.2Operating procedure3.2.1 CommissioningCommissioning procedure is important to be conducted prior starting up equipment for safety and quality assurance. The usual procedure for commissioning is carried as follows:

Operational check out list procedure [6]1. Locate all the instrumentation according to PID in the plant. 2. Check the control valve, globe valve, drain valves, vent or relief valve to ensure they are installed properly3. Review of all piping connection for any steam tracing or any deposit.4. Check for the bypass line installation around the pipeline of the equipment to ensure it is already been installed.Hydrostatic test [7]1. It is carried out on the flash tank to prove the strength of the materials and weld integrity after construction had been completed. 2. Locate the pressure within a sealed vessel.3. Fill the vessel with incompressible fluid like water4. Subject the pressure to a known internal pressure which is typically 150% than the maximum operating pressure for 2 hours; the large internal pressure applied will cause the expansion of the vessel.5. Read the instrumentation that attached to the pressure to determine the total and permanent expansion that the test chamber (external) undergoes.6. Carry out physical and visual inspection to determine the condition of the vessel being tested.7. If the vessel did not pose any damage or being permanent distorted due to test pressure, then the equipment can proceed to start up procedure. Start up1. Ensure the flash vessel is totally empty and free of any foreign objects.2. Flush the unwanted material in the vessel using slurry and drain the wastes via drain valve if the vessel is not empty3. Ensure the vessel is connected to all the utilities and check for any possible loosen pipe connection to the vessel to prevent leakage of slurry. 4. Ensure the temperature, pressure and level sensors attached to the vessel functioning properly.5. Run the utilities and ensure the operating condition like pressure and slurry pool level in vessel is achieved through the control system6. Monitor the flash vessel for about 30 minutes to check for any unusual activities. 7. If everything is under good operating condition, feed the slurry into the flash column; otherwise check for any issue that limit the desired operating condition from being achieving.

Shut down1 If the operation is to be shut down, it is recommended to close the feed valve to stop feeding the vessel.2 Turn off all the operating switches.3 Drain off the slurry from the flash vessel and vent off the possible vapor build in the vessel.4 Ensure the vessel is totally empty.5 Slowly depressurizing the vessel to atmospheric pressure by turning on the relief valve.6 Shut down all utilities connection. 7 Allows the vessel to be cooled down to room temperature.8 Check for any possible equipment damage or leakages.9 Inform the maintenance team for any possible damage to the equipment. Operating procedure1. Control the flow meter so that 1212.15 kg/s is achieved in the feed stream.2. Ensure the slurry level in flash tank is always maintained at the required level and as well the pressure in vessel is constant at 263.54 kPa.3. Ensure the slurry inlet temperature to flash tank is of 145oC to ensure optimum flashing of vapor under desired operating pressure in flash tank as temperature will change the VLE equilibrium of flash pressure. 4. Carry out close monitoring to the flash vessel operating condition and check for any unusual activity.5. Perform emergency shutdown procedure if serious problem arise to the operating vessel and hard to solve it. Emergency shut downIn an event of emergency shutdown, recognized the vessel alarms and acted upon.1. Take immediate action if excessive temperature, pressure or low liquid level is observed.2. Stop the feeding of slurry into the vessel.3. Open the drain and vent valves to release the caustic liquid and as well as depressurizing.4. No entry or work should be done on the flash vessel before the vessel is free of slurry and depressurized. Maintenance and cleaning measureAs routine maintenance or cleaning to flash vessel is required to ensure smooth operation of process flow, it is recommended that the following requirements listed below achieved before any maintenance work carried out:1. Isolate electrical power and mechanical drives. 2. Source of heat and corrosive caustic soda isolated.3. Preliminary check up for the condition of pipeline, equipments itself for any hairline crack or any unfavorable dangerous event.4. Record the performance of the flash tank before and after the maintenance work has been done. 5. Check for fouling in flash tank and as well as piping connection.6. Readjust the control system of the flash tank to favor shut down.7. Check for the safe guard system and ensure it function properly and ready to function in emergency situation.Environmental accident response procedureLeakage of corrosive alkaline slurry from flash vessel or pipeline is hazardous to environment. Whenever, a spill or leakage is found:1. It is advisable that the workers wear protective personnel equipment to protect themselves from the liquid.2. Check for the size of the leak and perform clean up action as according to Table 6.3. Immediate action carried out by maintenance team to fix the broken pipeline or equipment.4. Isolate the flow of slurry into the affected pipeline or equipment. 5. Adjust control system to reduce or stop the operating equipment.6. Install pressure gauge on pipeline to detect any leakage through fluctuation of pressure.

3.3 Safety Study (HAZID)

HAZARDIDHAZARD CATEGORY (GUIDEWORD)HAZARD DESCRIPTION / HAZARDOUS EVENT

CONSEQUENCESPREVENTION / DETECTION / BARRIESRISK ASSESSMENTRECOMMENDATIONSACTIONS

LIKELIHOODCONSEQUENCESEVERITYRANKING

1

Natural DisastersExtreme heatPressure build up in FT-101

Heat stress of personnel

Pipeline an equipment thermal expansion

FT-101 operate higher than operating temperature of 138.26CShut down operation

Evacuate personnel from extreme heat

PossibleLowLowMonitor the operating temperature and pressure of FT-101

Install high temperature alarm on and pressure alarm on FT-101Operators to do temperature monitoring

Electrical engineering team to install alarms

Operators to inspect the equipment and pipeline condition.

2

External EffectsDropped objectsDamage of FT-101

Possible rupture of FT-101, thus release of corrosive caustic

Injury or death of the workers Inspect regularly for overhead equipment and possible loose items.

UnlikelyCriticalExtremeEnsure rigging is in good condition and operated correctly

Installation of safety netting above FT-101

Wearing protective hard hat and as well as personal protective equipmentsOffshore health and safety executive to handle all the safety requirement rule and regulations.

3

External EffectsFatigue/ cracking Rupture of pipeline

Loss of containment

Cracking of FT-101 shell

Loss of alumina productionN/AUnlikelyMajorHighPerform non destructive testing (NDT) on vessel to test vessel thickness and pipeline integrity

Visual inspection of any hairline crack on the equipment.

Maintenance engineering team to perform the testing and fix broken pipeline or equipment leakage.

4

Human FactorsImproper/inadequate trainingLoss of production

Process upset and abnormal operating condition

Damage to equipment which might include FT-101

Explosion N/A PossibleCriticalExtremeProvide adequate training for operators

Compulsory in preparing operating procedure manual by designers and the procedure have to be strictly obeyed

Designers/ consultants to provide the training.

Operators to obey the rule and regulations from the operating manual

5

Equipment/Instrumentation Malfunction

Control valve V-01 failureNo heat exchange (fail to open)

FT-101 over pressurized (fail to close)

Loss of containment (fail to close)N/AUnlikelyMajorHighInstall bypass valve to the control valve

Install isolation valves around valve V-01 for maintenance of broken V-01Process engineering team to design and maintenance team to install bypass and isolation valves

6Process UpsetsFlow deviation Increase in temperature in FT-101 Insufficient temperature to digest bauxite oreN/ALikelyModerateHighInstallation of flow control system at the outlet stream of spent liquorProcess engineering team to design and electrician to install the control system

7

Process UpsetsPressure deviation FT-101 over pressurized and rupture

Loss of containment

Upsets to downstream equipment

Personal injury or deathRelief valve V-04

PossibleCriticalExtremeInstallation of emergency shutdown valve and high temperature alarm.

Electrical engineering team to install emergency shutdown valve connected to high temperature alarm and display at the indicator

8

Process UpsetsCorrosion/ erosion Cracking and leakage of FT-101 and as well as inlet and outlet pipelines S019, S020, S021.

Cracking of vessel or pipelineNickel alloy steel materials for all the pipelines and tube side of FT-101LikelyMajorExtremeVisual inspection on the pipeline for any possible defects.

Frequent non destructive test for pipeline and vessel wall thickness Operators to perform the checking periodically.

Maintenance engineering team to perform the testing.

9Utilities FailuresLoss of powerLoss of functionality of cascade control systems

Pressure build up in FT-101

Loss of alumina productionFail open/closed valves UnlikelyModerateModerateBackup generator for important process equipmentElectrical engineering team to install backup generator

HAZOP Project: Alumina refineyDate: 27/4

P&ID No.: 0001Node No.: FT-101

Node Description: Flash Tank FT-101

HAZOP Lead: Kelvin Tan Khai YikHAZOP Scribe: Vincent Tan Kok Yeow

No.ParameterGuidewordPossible Cause (s)DeviationConsequenceSafeguard(Existing)RecommendationsAction

1.LevelNo1. No flow through inlet S019.2. More flow through liquid outlets S020.3. Major rupture in vessel FT-101 that caused loss of slurrySlurry cannot be cooled down properly (2)Improper separation of vapour and slurry (2)No production (1)Loss of production (3)Loss of containment (3)FT-101 shutdown procedure (1)Level control systems LIC-01 and LIC 05.Low level alarms (LLA 04)Bypass valve V-02 around I-3 (1)

Perform regular inspection and maintenance onto the equipment.

-Electrical Engineering to install alarms-Process engineering to install bypass valve-Operator to perform regular inspection -Maintenance team to repair the broken equipment.

2.LevelLess1. Less flow through inlet S019. 2. More flow through liquid outlets S-20.3. Rupture in vessel FT-101.Reduced product quality (2)No production (1)Loss of production (3)Loss of containment (3)Slurry cannot be cooled down properly (1,2)mproper separation of vapour and slurry (2)

Same as 1.Same as 1.Same as 1.

3.LevelMore1. More flow through inlet S019.2. Less flow through liquid outlets S020.Reduced product quality (1,2)Liquid carry over by vapour to outlet S021. (1,2)Slurry cannot be cooled down properly (1,2)Improper separation of vapour and slurry (1,2)

Same as 1.Liquid outlet bypass valves V-11 through I-1.Same as 1.Same as 1.

4.PressureLess1. Less pressure in inlet line S019.2. Less pressure in liquid outlets S020.3. Pressure relief valve V-04 fails to close completely4. Minor rupture in FT-101.5. Pressure controller PC-03 fails to close valve V-07.Slurry not effectively cooling down (1,2).Inefficient in flashing (1) .Multiphase flow occurs (2). Liquid hard to flow from one tank to another (2).Loss of production (4)Lead to deformation of vessel (3,4,5)Loss of containment (4).

Level controlPressure controller

Closely monitor the pressure in the flask tank. Install Vent. Same as 1.Same as 1

5.PressureMore1. More pressure in inlet line S019.2. More pressure in liquid outlets S020.3. Pressure relief valve V-04 fails to open4. More pressure in gas outlet line S-21.Increase the temperature of slurry (1, 2).Transportation flow issue of slurry from one tank to tank (2).Rupture in FT-101 (1,2,3,4)Reduced product quality (1,2,3,4)Level control systems LIC-01 and LIC 05.Pressure relief valve V-04 (1,4)Pressure controller PC-03 (1,4)Manual bypass of RV-01 with V-02 (3,4)FT-101 shutdown procedure (1,2,3,4)High pressure alarm to give notificationSame as 4.Same as 4

6.FlowNo1. No flow in Inlet line S-19.2. No flow in liquid outlets S020.3. No flow in gas outlet line S021.No production (1,2,3)Build of liquid in FT-101 (2)Pressure build up in FT-101 (3)Level control systems LIC-01 and LIC-02 (2)Liquid outlet bypass I-1.FT-101 shutdown procedure (1,2,3)Pressure relief valve V- 04 (3)Pressure control system PC-03 (2)Low level alarm to notify (2)Same as 1Same as 1.

7.FlowLess1. Less flow in Inlet line S-19.2. Less flow in liquid outlets S020.3. Less flow in gas outlet line S021.Less production (1,2,3)Build of liquid in FT-101 (2)Pressure build up in FT-101 (3)As 6.Same as 1.Same as 1.

8.FlowMore1. More flow in Inlet line S-19.2. More flow in liquid outlets S020.3. More flow in gas outlet line S021.Reduced product quality (1,2,3,4)No production (4)Loss of containment (4) Damage to equipment upstream and downstream of FT-101 (1,2,3)FT-101 shutdown procedure (1,2,3,4)Level control systems LIC-04 and LIC-02 (2)Pressure relief valve V-04. (3)Pressure control system PC-03. (3)notify.Same as 1.High level alarm to notify (2). High pressure alarm to notify.Same as 1

9.TemperatureLess1. Low pressure in FT-101.2. High pressure inlet stream S019.3. Changes in atmospheric conditions4. High temperature inlet stream S019.Inefficient separationCondensation of vapourSlurry is hard to flash cooled.Pressure control system PC-03 (1)FT-101 shutdown procedure (1,2,3,4)Installation of temperature control system TI-01Installation of low temperature alarm connected to TI-01Same as 1

10.TemperatureMore1. High pressure in FT-1012. Low pressure inlet stream S019.3. Changes in atmospheric conditions4. High temperature inlet stream S019.Inefficient separationCondensation of vapour

Pressure relief valve RV-01 (1)Pressure control system PC-01 (1)FT-101 shutdown procedure (1,2,3,4)Installation of temperature control system TI-01Installation of high temperature alarm connected to TI-01Same as 1

11.Maintenance 1. Cracks/leakage of vessel FT-1012. Failure of inlet valve V-02.3. Failure of pressure relief valve V-04.4. Failure of slurry outlet valve V-11Required shutdown (1,2,3,4,5,6)Requires replacement of FT-101 (1,2,3)By pass valve I-3 for inlet 02.Isolation valve V-01, V03 to serve the purposes of maintenancePressure indicator on FT-101 to indicate the vessel pressure.Same as 1.Pressure indicator on FT-101 to indicate the vessel pressure.Same as 1

4.0 Mechanical designFor mechanical design, the flash column is designed as a thin walled pressure vessel under internal pressure. The mechanical design for the vessel proposed will be based on the data in process calculation and with some safety consideration added to the design temperature, pressure, material of construction and corrosion allowance. The components to be designed as listed as follows:1 Orientation of pressure vessel2 Type and thickness of head and end closure3 Minimum wall thickness for the cylindrical pressure vessel body4 Dead weight of vessel5 Analysis of stresses6 Elastic stability check7 Skirt support8 Base ring and anchor bolts9 Pressure test The operating condition for the flash vessel is 263.54kPa and 138.26oC. Nickel alloy 400 is used for the vessel body construction. It might be a costly decision to choose alloy however with the consideration of corrosive caustic medium and carbon steel only work well in the medium up to temperature of 77oC, alloy 400 is chosen. Double welded butt which are fully radiographed is used and gives a joint factor, J=1. Corrosion allowance is 4mm for corrosive medium [3]. Pressure vessel orientation and type of head used and as well as closure end [3]Vertically flash vessel is employed due to the reason of low feed capacity, low liquid hold up time where the residence time is not the main factor in alumina refinery. The orientation favor the transport of fluid from one tank to another by mean of gravitational force and pressure differential. Conical bottom head are used in the design as it is generally for low pressure application 2.64 bar and excessive material thickness are avoided. Advantages of the conical head to dishes head is of minimizing the potential formation of stagnant fluid zones in relation to the discharge of fluids from the flash vessels. The design formula for conical bottom is as follows:t = = = 5 mmDue to time constraint, the design stress for nickel alloy 400 is assumed to be the same as low alloy steel. With design angle of 60oC as suggested by HATCH, and 10% extra above calculated temperature and pressure for safety design purposes, the designed temperature and pressure is as follows: Design temperature = 138.26 x 1.1 = 152.09oC Design pressure = 263.54 x 1.1 = 289.89kPa = 289.89 x 0.001 = 0.2899 N/mm2The design stress with reference to temperature from table 13.2 = 240 N/mm2The calculated wall thickness for conical bottom is 5mm and with corrosion allowance, 5mm + 4mm = 9mm Cylindrical shell Minimum wall thickness, Add corrosion allowance 2.48 mm + 4 mm Dead weight of vessel [3]For cylindrical steel vessel with domed ends, uniform wall thickness,(Sinnott 2001)WV=240CVDm(HV+0.8Dm)t =240(1.08)(4.110+9x10-3)[7.19+0.8(4.11+9x10-3)](9) =72523.51N where:CV=1.08 with vessels with only few internal fittingsDm=mean diameter of vessel (Di+t)HV=length of cylindrical sectiont=wall thickness,mmAssume the ladder length is 7.19m for maintenance purposes, For plain steel ladder, 150N/m x 7.19m = 1078.5NTotal weight = 1.08 + 72.52 = 73.6kNAnalysis of stresses [3]

Figure 5 Stresses in a cylindrical shell under combined loading [3]. At bottom tangent linePressure stresses: Longitudinal stresses, Circumferential stresses, Dead weight stress: Bending stresses: D0=4110+2x6.48=4122.96mmSecond moment of area of the vessel about the plane of bending,

Total bending moment at the plane being considered,

where:Dynamic wind pressure = 1280N/m2 (Sinnott 2001)Mean diameter = 4.11+2(6.48)x10-3=4.12mLoading(per linear meter), FW =1280x4.12=5277.4N/m

Bending stress,

The resultant longitudinal stress is:

= 46.60 N/mm2

47.04

91.88

Figure 6 Principal stresses on up-wind side [3]

Greatest difference between principal stresses =91.88 47.04 = 44.84 N/mm2Satisfactory since greatest difference between principal stresses is below the maximum allowable design stress (240N/mm2). Elastic stability check (Buckling) [3]Critical buckling stress: The maximum compressive stress will occur when the vessel is not under pressure,=As the calculated value is below critical buckling stress, the design is satisfactory. Skirt support [3]Skirt support is to be designed in the way that it is able to support the maximum dead weight load of the vessel when it is completely filled with water. For a straight cylindrical skirt, Assume skirt height = 2mApproximate weight = ( x D2 x L) g = Weight of vessel= 72.52kNTotal weight=935+72.52=1007.52kNWind loading=5.28 kN/mBending moment at base of skirt, Ms= Fw x ()

As first trial, skirt thickness is to be taken the same as bottom section of vessel = 6.48mmBending stress in the skirt, Dead weight stress in the skirt, Maximum Maximum

Take joint factor J as 0.85.Criteria for design: 0.425(240)(0.85)sin900 0.425204The young modulus for low nickel steel is 185469.04 N/mm2 at 138oC [13] 13.31 13.31 225where: E(Youngs modulus at ambient temperature, N/mm2)

Since both constraints are satisfied, and add 4 mm for corrosion the design skirt thickness (ts) is 6.48+4 = 10.48 mmBoth criteria are satisfied, add 2mm for corrosion, and give a design skirt thickness (ts) of 12mm.

Figure 7 Typical straight skirt support design [3]Base ring and anchor bolts [3]To transmit loads to the foundation slab, base ring is typically used with skirt support. The anchor bolts tensile load works to withstand external pressure from overturning the vessel (Sinnott 2001). Approximate pitch circle diameter, say 2.1mCircumference of bolt circle= 2100Number of bolts required, at minimum recommended bolt spacing =Closest multiple of 4 =12 boltsTake bolt design stress= 125N/mm2Ms =111.48 kNmTake W = operating value = 72.52 kNBolt area required,

Bolt root diameter= Small as it < 25mmTotal compressive load on the base ring per unit length,

Taking the bearing pressure as 5N/mm2.The minimum width of the base ring, Lb=(size is small)As the calculated root diameter and minimum width of base ring is too small, the smallest bolt size is chosen.

Use M24 bolts (BS 4190:1967) root area=353mm2Actual width required=Lr+ts+50mm =76+6.48+50 =132.48 mm50mm is the allowance space.Actual bearing pressure on concrete foundation: Base ring minimum thickness, where:fr = allowable design stress in the ring material, and the basic design stress is 140N/mm2

Figure 8 Flange ring dimensions [3]

Figure 8. Figure 9 Standard bolt size M24 and dimensions [3]

Pressure test [3]Based on BS5500, for the proving of the integrity of vessel, test pressure of 30% above the design pressure is used..Test pressure=1.3 x 0.29N/mm2= 0.38N/mm2Design stress at test pressure, fa=

The vessel design is valid since the calculated design stress 73.48 is below the permissible stress 240N/mm2.

4.1 Mechanical Drawing

Figure 10 Flash tank mechanical design

5.0 Critical Review Flash Tank

The designed flash tank is sized in vertical arrangement and it has the diameter of 4.1and height of 7.25m and slurry pool height of 1.45m. The flash tank dimension is reliable as HATCH provided all the information needed for the sizing. The main concern with the flash tank design is the transportation flow of fluid from one tank to another. It is to ensure that the hydraulic head does not incur multiphase flow in pipeline to minimize erosion. However, due to time constraint the report did not show the design on hydraulic fluid transport. In addition, the valve sizing is also has been ignored due to time management problem. Modelling of slurry flow can be done on the particular flash tank in order to study better the efficiency of the flash tank and how the fluid behave in the tank.

Heat Exchanger The design heat exchanger is of one shell two tube passes. The shell side of the heat exchanger is of condenser configuration where the formula involves for the calculation of heat transfer coefficient and pressure drop are with the consideration of multiphase flow (condensing vapor) happening at the outer tube of shell. However, the design equation proposed is not accurate as Kern method is employed. There are other method like Bell method and Delaware method which can be used for the sizing of heat exchanger as they provide more accurate pressure drop and with the consideration of baffle to shell and tube to baffle leakages and as well as bypassing. The proposed design also without consideration of venting non condensable air as in actual case there are non-condensable air exists in heat exchanger that reduce the performance of overall heater. If I had to design it again, I would take that into consideration and use sophisticated software to predict the performance of heat exchanger.

References [1] Experiment 14. 2014. PERFORMANCE EVALUATION OF A SHELL AND TUBE HEAT EXCHANGER. Accessed November 10. http://www6.kfupm.edu.sa/heattransfer/Expt_14_Shell%20and%20Tube%20HX%20Exp.pdf[2] Kenmneth J. Bell. 1996. Thermal and hydraulic design of heat exchangers. Begell house: New York.

[3] Sinnot, R. K. 2005. Coulson & Richardsons chemical engineering volume 6. 4th ed. Oxford: Elsevier Butterworth-Heinemann. [4] Droy, Bernard and Dany Michaux. 2012. Bauxite ore digestion in the bayer process. Accessed November 11,http://www.google.com/patents/US6555076[5] Lowy, Gunnewiek and Umesh Shah. 2008. Flash Vessel Process Design. International Conference CFD in Oil & Gas, Metallurgical and Process Industries. [6] KLM Technology Group.2011. START-UP SEQUENCE AND GENERAL COMMISSIONING PROCEDURES.http://www.klmtechgroup.com/PDF/ess/PROJECT_STANDARDS_AND_SPECIFICATIONS_general_commissioning_procedures_Rev01.pdf[7] Engineer Edge. 2000. Hydrostatic engineering review. http://www.engineersedge.com/testing_analysis/hydrostatic_testing.htm[8] Environmental Health and Safety. 2014. Chemical Spills Procedure. Accessed November 12http://web.princeton.edu/sites/ehs/emergency/spills.htm[9] Kuppan Thulukkanam. 2013. Heat Exchanger Design Handbook, Second Edition. CRC Press: United State. http://books.google.com.au/books?id=ZsU5A1mANWUC&pg=PA1169&lpg=PA1169&dq=operating+procedure+for+heat+exchanger+start+up+and+shut+down+and+maintenance&source=bl&ots=sa4DzDG-y8&sig=SH-eqbnSp17o2ZVYEh83Ozae3WM&hl=en&sa=X&ei=k_FdVObBH-TAmQXT74CQDw&redir_esc=y#v=onepage&q=operating%20procedure%20for%20heat%20exchanger%20start%20up%20and%20shut%20down%20and%20maintenance&f=false[10] Types of vessel head. 2013. Mycheme. Accessed November 11.http://www.mycheme.com/types-of-vessel-head/[11] Liptak, B. G. 2005. Heat Exchanger Control and Optimization. http://books.google.com.au/books?id=TxKynbyaIAMC&pg=PA2004&lpg=PA2004&dq=the+transfer+of+heat+is+one+of+the+most+basic+and+best+understood+unit+operation+of+the+processing+industries.+Heat+can+betransferred+between+the+same+phases&source=bl&ots=jxqhQPdxDP&sig=7t4w5QQADVWp9T9XLmVdanl4_0&hl=en&sa=X&ei=V0xkVLqbBOXlmAWgqIDQAg&ved=0CB8Q6AEwAA#v=onepage&q=the%20transfer%20of%20heat%20is%20one%20of%20the%20most%20basic%20and%20best%20understood%20unit%20operation%20of%20the%20processing%20industries.%20Heat%20can%20betransferred%20between%20the%20same%20phases&f=false[12] Module 2. 2014. Mechanical Design Standards. Accessed November 11. http://nptel.ac.in/courses/103103027/[13] The Engineering Toolbox. 2014. Young Modulus of Elasticity for Metals and Alloys. Accessed November 11, http://www.engineeringtoolbox.com/young-modulus-d_773.html