final report on spent solution in hydro

INTRODUCTION

1.1 Scope

To study the basic operation of control room .To study cooling tower and determine cooling tower efficiency. Selecting the right cooling tower structure and material..To study the type of the fan and material is used in cooling tower. To improve efficiency of exhaust.. To determine flow rate of spent ( acidic zinc sulphate solution ).Maintenance and cleaning requirements in cell house area.

1.2 Methodology

Study which type of cooling tower is being used, study its type of structure for cooling tower, components of cooling tower (air inlet, drift eliminators, fans, tower materials).For mathematical calculation of cooling efficiency of cooling tower calculate inlet temperature ,outlet temperature, wet bulb temperature and obtain multiple readings and take average of all the readings Study type of blades ,blade material, capacity of face cooler, material requirements ,laws of fan, characteristics of fan, maintenance and cleaning requirements in cell house .Study basic leaching process ( acidic zinc sulphate solution), type of material used on which volumetric flow of spent take place(corrosive or non corrosive), calculate flow rate manually ,take multiple readings and take mean of all the readings.

2 COOLING TOWER

2.1Introduction

Cooling towers are a very important part of many industries. The primary task of a cooling tower is to reject heat into the atmosphere. They represent a relatively inexpensive and dependable means of removing low-grade heat from cooling water. The make-up water sources used to replenish water lost to evaporation. Hot water from heat exchangers is sent to the cooling tower. The water exits the cooling tower and is sent back to the exchangers or to other units for further cooling.

Fig no. 1 closed loop cooling tower system [1]

2.2 Types of cooling tower

Cooling towers fall into two main categories: Natural draft Mechanical draft.

Natural draft towers use very large concrete chimneys to introduce air through the media .Due to the large size of these towers, they are generally used for water flow rates above 45,000m3/hr. These types of towers are used only by utility power stations. Mechanical draft towers utilize large fans to force or suck air through circulated water. The water falls downward over fill surfaces, which help increase the contact time between the water and the air - this helps maximise heat transfer between the two. Cooling rates of Mechanical draft towers depend upon their fan diameter and speed of operation. Since, the mechanical drift cooling towers are much more widely used, the focus is on them in this chapter.

Mechanical draft towers are available in the following airflow arrangements

1. Counter flows induced draft.2. Counter flow forced draft.3. Cross flow induced draft.

In the counter flow induced draft design, hot water enters at the top, while the air is introduced at the bottom and exits at the top. Both forced and induced draft fans are used.

In cross flow induced draft towers, the water enters at the top and passes over the fill. Their, however, is introduced at the side either on one side (single-flow tower) or opposite sides(double-flow tower). An induced draft fan draws the air across the wetted fill and expels it through the top of the structure.

The Figure 2 illustrates various cooling tower types. Mechanical draft towers are available in a large range of capacities. Normal capacities range from approximately 10 tons,2.5 m3/hr flow to several thousand tons and m3/hr. Towers can be either factory built or field erected - for example concrete towers are only field erected. Many towers are constructed so that they can be grouped together to achieve the desired capacity. Thus, many cooling towers are assemblies of two or more individual cooling towers or "cells." The number of cells they have, e.g., an eight-cell tower, often refers to such towers. Multiple-cell towers can be lineal, square, or round depending upon the shape of the individual cells and whether the air inlets are located on the sides or bottoms of the cells.

Fig 2 Types of cooling tower [1]

2.3 Description and design features

The ZACT (zincobre atmospheric cooling tower) is based on following characteristics.

Design PLS Max flowrate per unit 165 m3/hr

Normal flowrate per unit 138 m3/hrInlet temperature Max 80 °C

Outlet temperature 34°C

Design wet bulb temperature 28°C

Cooling air flow Max 360000 m3/hr

2.4 Operating principle

A cooling tower may be consider as a heat exchanger in which liquid and air are in direct contact with on another. Heat is transferred from liquid drops to surrounding air by the transfer

of sensible latent heat. and Liquid is sprayed into the air at the top of the tower. Counter flow cold air comes from exterior and passes through the tower volume .The Mist Eliminator Module filters the exhaust hot air to avoid the environmental contamination and to reduce the loss of liquid by evaporation. The heat transference is produced by the different enthalpy of air and liquid. The transference depends on the contact surface among many other factors ( in liquid temperature, wet bulb temperature, liquid flow rate, air flow etc). The surface of contact depends on the size of sprayed drops. The aim of the ACT is to improve overall parameter to increase heat transfer coefficient. This leads us to change the traditional square shape ,with poor efficiency near the corners, to a circle shape, with a homogeneous distribution of air and liquid flows. On the other hand, the tower height depends upon the necessary time of contact between the liquid drops and the air. The liquid coming out of the nozzles takes some length to achieve the good distribution inside the tower. Then, it needs time transfer the heat to the counter flow air. Thus, for the present design, the height of the cooling tower was chosen to ensure that all these requirements are met an oversize of 15%. To ease the manufacturing process, the circle shape is achieved with a regular octagon made of flat walls (panels) . There are two aspects that condition the dimensions of this “ circle” shape: the fan dimensions and mainly, the room needed to spread the liquid flow inside the tower properly. The pressure of the liquid and its viscosity determines the droplet size and spreading characteristics of a nozzle. Since the viscosity of the liquid does not suffer almost any change by the content of solids, the dimension of octagon does not change from a Zn electrolyte solution cooling tower..Tangential flow full cone spraying nozzles are used to achieve an extremely uniform area distribution of the sprayed liquid.

The important parameters, from the point of determining the performance of cooling towers, are:

i) "Range" is the difference between the cooling tower water inlet and outlet temperature.

ii) "Approach" is the difference between the cooling tower outlet cold water temperatureand ambient wet bulb temperature. Although, both range and approach should be monitored,the 'Approach' is a better indicator of cooling tower performance.

iii)"Range" is the difference between the cooling tower water inlet and outlet temperature

2.5 Cooling Tower EfficiencyThe cooling tower efficiency can be expressed as

μ = (ti - to) 100 / (ti - twb)

where

μ = cooling tower efficiency (%)

ti = inlet temperature of water to the tower (oC, oF)

to = outlet temperature of water from the tower (oC, oF)

twb = wet bulb temperature of air (oC, oF)

Fig no. 3 Graphical representation of the cooling tower characteristics [3]

Fig no. 4Actual cooling tower structure in plant [2]

TableATMOSPHERIC COOLING TOWER COMPONENTS

MAIN ASSEMBLY

SECONDARY ASSEMBLY

DRAWINGS IDENTITY NO.

PIPE & SPRAYING SYSTEM

HEADERS 1

CAMLOCKS 2

FEXIBLE HOSE 3

FLANGED ELBOW 4

NOZZLE

PP DISTRIBUTION RING

5

PP FEEDING PIPE

PIPE SUPPORTS

WALKWAYS GRATING MESH

GRATING FRAME

SUPPORT OF WALKWAY

HANDRAL

FAN BLADES (6) 6

HUB 7

GEAR MOTOR 8

GEAR MOTOR SUPPORT

9

FAN PILLAR 10

MIST ELIMINATORS MODULES (MEM)

MIST ELIMINAT FOR BLADES

11

STEEL STRUCTURE 12

FRP LATERAL PANELS

13

STRUCTURE FRP LATERAL PANELS

14

AIR DUCT 15

Fig no. 5 Schematic structure of forced cooling tower [2]

2.6 Methodology

Take thermometer clean its bore using cotton. Using thermometer first take inlet temperature of spent ( acidic zinc sulphate solution)

which is pumped from tank house ( contains acidic zinc sulphate solution coming after electrolysis) using centrifugal pump to the cooling tower.

Now measure temperature of spent solution coming out from cooling tower in an open runnel.

Take cotton dip into tap water and attach to bore of thermometer and whirl in air of cell house area and note down wet bulb temperature.

Take multiple reading in an interval of a hour. Calculate cooling tower efficiency for each time and take mean efficiency and it should

be in between desired cooling tower efficiency according to plant design parameter

Note1. Reading was taken on 9th day after scheduled cleaning and maintenance ( in every 15 days) of cooling tower in an interval of a hour.

OBSERVATION TABLE NO. 1

Sr. no. Parameters Value 1 Type Forced draft 2 Tower size(diameter) 6700mm3 Impeller fan (diameter) 3962mm4 Air flow rate 96 m3/s5 Pressure 90 pa6 No. of blades 67 Power 37kw8 Supply voltage 415v 50 hz9 Fan speed 250 rpm

OBSERVATION TABLE NO.2

Sr no.

Inlet (ti )Temperature

Outlet (to )temperature

Wet bulb (twb )temperature

Cooling efficienciy(μ %)

1 52.1 34.3 30.1 80.902 52.2 34.5 29.8 79.013 52 34 30 81.814 52.8 34.6 30.3 80.805 53 35 30.8 81.08

Mean efficiency 80.72

2.7 Tower material

In the early days of cooling tower manufacture, towers were constructed primarily of wood.Wooden components included the frame, casing, louvers, fill, and often the cold water basin. If the basin was not of wood, it likely was of concrete. Today, tower manufacturers fabricate towers and tower components from a variety of materials. Often several materials are used to enhance corrosion resistance, reduce maintenance, and promote reliability and long service life. Galvanized steel, various grades of stainless steel, glass fiber, and concrete are widely used in tower construction as well as aluminum and various types of plastics for some components. Wood towers are still available, but they have glass fiber rather than wood panels (casing)over the wood framework. The inlet air louvers may be glass fiber, the fill may be plastic, and the cold water basin may be steel. Larger towers sometimes are made of concrete. Many towers–casings and basins–are constructed of galvanized steel or, where a corrosive atmosphere is problem, stainless steel. Sometimes a galvanized tower has a stainless steel basin. Glass fiber is also widely used for cooling tower casings and basins, giving long life and protection from the harmful effects of many chemicals. Plastics are widely used for fill, including PVC, polypropylene, and other polymers. Treated wood splash fill is still specified for wood towers, but plastic splash fill is also widely used when water conditions mandate the use of splash fill. Film fill, because it offers greater heat transfer efficiency, is the fill of choice for applications where the circulating water is generally free of debris that could a plug the fill passage ways. Plastics also find wide use as nozzle materials. Many nozzles are being made of PVC, ABS,polypropylene, and glass-filled nylon. Aluminum, glass fiber, and hot-dipped galvanized steel are commonly used fan materials. Centrifugal fans are often fabricated from galvanized steel. Propeller fans are fabricated from galvanized, aluminum, or moulded , glass fiber reinforced plastic.

2.8 Maintenance operation on cooling tower

This section lists the most important options to improve energy efficiency of cooling towers.

Follow manufacturer’s recommended clearances around cooling towers and relocate or modify structures that interfere with the air intake or exhaust.

Optimize cooling tower fan blade angle on a seasonal and/or load basis. Correct excessive and/or uneven fan blade tip clearance and poor fan balance.

In old counter-flow cooling towers, replace old spray type nozzles with new square spray nozzles that do not clog.

Install nozzles that spray in a more uniform water pattern Clean plugged cooling tower distribution nozzles regularly Balance flow to cooling tower hot water basins Control cooling tower fans based on exit water temperatures especially in small units Check cooling water pumps regularly to maximize their efficiency The following maintenance operations will be carried out in every 15 days:

1 Spears and nozzle cleaning2 substituting drift eliminator3 cleaning of drift eliminator4 collecting basin cleaning and flushing

3 COOLING TOWER FAN

3.1Introduction

Fans provide air for ventilation and industrial process requirements. Fans generate a pressure to move air (or gases) against a resistance caused by ducts, dampers, or other components in a fan system. The fan rotor receives energy from a rotating shaft and transmits it to the air.The purpose of a cooling tower fan is to move a specified quantity of air through the system, overcoming the system resistance which is defined as the pressure loss. The product of air flow and the pressure loss is air power developed work done by the fan; this may be also termed as fan output and input kW depends on fan efficiency. The fan efficiency in turn is greatly dependent on the profile of the blade. An aerodynamic profile with optimum twist, taper and higher coefficient of lift to coefficient of drop ratio can provide the fan total efficiency as high as 85–92 %. However, this efficiency is drastically affected by the factors such as tip clearance, obstacles to airflow and inlet shape, etc. As the metallic fans are manufactured by adopting either extrusion or casting process it is always difficult to generate the ideal aerodynamic profiles. The FRP blades are normally hand moulded which facilitates the generation of optimum aerodynamic profile to meet specific duty condition more efficiently. Cases reported where replacement of metallic or Glass fibre reinforced plastic fan blades have been replaced by efficient hollow FRP blades, with resultant fan energy savings of the order of 20–30% and with simple pay back period of 6 to 7 months. Also, due to lightweight, FRP fans need low starting torque resulting in use of lower HP motors. The lightweight of the fans also increases the life of the gear box, motor and bearing is and allows for easy handling and maintenance.

3.2Scope

The application covers the technical requirements of the cooling tower fans for cooling gypsum saturated spent solution in the tank house

3.3 Types of axial flow fan

Tubeaxial:-fans have a wheel inside a cylindrical housing, with close clearance between blade and housing to improve airflow efficiency. The wheel turn faster than propeller fans, enabling operation under high-pressures 250 – 400 mm WC. The efficiency is up to 65%.

Vaneaxial:- fans are similar to tubeaxials, but with addition of guide vanes that improve efficiency by directing and straightening the flow. As a result, they have a higher static pressure with less dependence on the duct static pressure. Such fans are used generally for pressures up to 500 mmWC. vaneaxials are typically the most energy-efficient fans available and should be used whenever possible.

Propeller:- fans usually run at low speeds and moderate temperatures. They experience a large change in airflow with small changes in static pressure. They handle large volumes of air at low pressure or free delivery. Propeller fans are often used indoors as exhaust fans. Applications include air-cooled condensers and cooling towers. Efficiency is low approximately 50% or less.

Fig no.6 Types of axial fans [1]

AXIAL-FLOW FANS

Type Characteristics Typical applicationsPropeller Low pressure,

high flow, low efficiency, peak efficiency close to point of free air delivery ( zero static pressure)

Air-circulation, ventilation, exhaust

Tube- axial Medium pressure, high flow, higher efficiency than propeller type, dip in pressure flow curve before peak pressure point

HVAC, drying ovens, exhaust systems

Vane- axial High pressure, medium flow, dip in pressure-flow curve, use of guide vanes improves efficiency exhausts

High pressure applications including HVAC systems

3.4 Design criteria in plant

DutyThe equipment shall be suitable for continuous operation,24 hours a day, all year around under following conditions:

Continuous operation at extremes of ambient temperature Continuous operation in an external environment containing high level

of acid mist Continuous operation fully exposed to the elements High-pressure hose washdown with the fan stopped

3.5 Design life

Number of towers 10Number of fans 1 per cellType Forced draftTower size( diameter) 6.74mFan suction Acid mist from tank house, direct suction

3.6Environmental design conditions

Dry bulb temperature 37°CWet bulb temperature 28°CAnnual rainfall 850mmEnvironment So2/so3 mistDesign wind speed 47 m/sSeismic zone II

3.7 Main design parameter

Air flow rate 100m2 /sImpeller diameter 3.962mTurning speed 250/minMinimum static pressure 90psNumber fan blades 6 unts.

3.8 Technical specification

The spent cooling towers are designed to cool gypsum saturated electrolyte, which is circulating in a zinc electrolysis. The cooling towers shall operate in parallel.

Particular attention has to be paid to the protection of the fan against acid mist, since the air for cooling is selected from tank house. This air is loaded with acid mist. A protection can be realized via drive casting, which has an opening for the fan shaft and another to suck the needed outdoor air for the drive cooling.

Forced draught cooling towers are formed by a vertical cylindrical body with the spray nozzles and the mist eliminators on top and the basin and the horizontal cylindrical fan duct on bottom. Gypsum saturated spent solution will be fed under pressure to the spray manifold, on top of cooling tower. Several nozzles will spray the GSPS into the tower, where a counter flow air stream will cool it down. The resulting cooled spent solution including the precipitated gypsum will be collected in a basin at the tower’s base and cleared through the hole at the bottom.

The towers are erected on a concrete basin . No fill (package) is intended inside the cooling tower due to the expected gypsum scale on the internal components.

Fans geared motors will be located on top of approx. 3.5m high concrete pillar, which will be braced to avoid resonance phenomenon. Fan’s hubs will be directly coupled to the output shaft of the gearboxes.

3.9 Fan suction side:

The fan will be located inside an horizontal cylindrical duct, which will link the tank house to the inside of the cooling tower. The duct shape will be cone. Cooling towers suck air from the electrolysis. A safety grid (approx 95% clearness) will cover all surface the duct inlet

The cooling towers in two lines of five are located parallel (approx. 17.5 m in between) with the fan suction sides looking east and west

3.10 Fan discharge side:

There are two important pressure drops of the air, one caused by the spraying purified solution inside the cooling tower and the other one caused by the mist eliminator layers.

There are two mist eliminator layers with approx 30.5 m2 free way section through each one. This area could be reduced by 10% due to gypsum build up.

3.11 Fan characteristics

The following table shows, as an example, the air flow that corresponds to each fan speed in a real ACT. These values are only for the selected fan (for specific, diameter, blade tip angle, fan type, obstacles and crosswind).This table may be helpful for plant operator to

estimate the air corresponding. The second graph shows, for the same fan how static pressure decreases with fan rpm

Fan rpm Air m3 /s Pressure (pa)250 95 80245 92.5 75.9240 90 71.8235 87.5 67.8230 84.9 64225 82.4 60.1220 79.8 56.4215 77.2 52.8210 74.5 49.2200 69.1 42.3190 63.5 35.7180 57.7 29.5170 51.5 23.5160 44.8 17.8

150 37.2 12.3145 32.8 9.5

Graph no.1 [2]

Graph no. 2 [2]

3.12 Fan laws

The fans operate under a predictable set of laws concerning speed, power and pressure. A change in speed (RPM) of any fan will predictably change the pressure rise and power necessaryto operate it at the new RPM.

Fig no. 7 Fan laws [2]

3.13 Fan design and selection criteria

Precise determination of air-flow and required outlet pressure are most important in proper selection of fan type and size. The air-flow required depends on the process requirements; normally determined from heat transfer rates, or combustion air or flue gas quantity to be handled. System pressure requirement is usually more difficult to compute or predict.Detailed

analysis should be carried out to determine pressure drop across the length, bends, contractions and expansions in the ducting system, pressure drop across filters, drop in branch lines, etc. These pressure drops should be added to any fixed pressure required by the process (in the case of ventilation fans there is no fixed pressure requirement). Frequently, a very conservativeapproach is adopted allocating large safety margins, resulting in over-sized fans which operate at flow rates much below their design values and, consequently, at very poor efficiency.Once the system flow and pressure requirements are determined, the fan and impeller type are then selected. For best results, values should be obtained from the manufacturer for specificfans and impellers. The choice of fan type for a given application depends on the magnitudes of required flow and static pressure. For a given fan type, the selection of the appropriate impeller depends additionally on rotational speed. Speed of operation varies with the application. High speed small units are generally more economical because of their higher hydraulic efficiency and relatively low cost. However, at low pressure ratios, large, low-speed units are preferable.

3.14 Material required

The fan’s hub and all its parts (including fasteners) shall be made of stainless steel, grade ASI 316 or better

Fan blades shall be made of a fibre reinforced resin. These should be suitable to withstand acid mist passing through the fan in a continuous operation. The manufacture shall provide information about these construction materials.

3.15 Maintenance operation on fan

Operation Condition/ frequency

Procedure Specific safety rule

Inspection of blades possible deposits

and damages

Once in every month

Proper lubrication, prevent breakdown

from vibrations, moisture and

fouling

During the performance of

maintenance activities at the fan, the impeller should be fastened and the electric connection of e- motor should

be disconected Impeller: paint inspection to

prevent corrosin

Atleast once a yearNew paint coating if it is damaged corroded away. paint type shall be at least equal to the original paint

Do not start any maintenance

activities until the fan has been

shutdown and it is dead. This shall be done such that the power cannot be

switched on unintentionally or inexpertly during

maintenanceImpeller :verifiicat

ion of tightening tourque of the bolts connections. blades angle verification

At least once a year When starting up the fan again, all legal

requirements regarding safety

distances from both live and rotating

parts and regarding safety guard shall be compiled with

Impeller:to replace corroded bolts and

nuts in time

Atleast once a year Visiual inspection:Replacement if

required

4 FLOW RATE OF SPENT (ACIDIC ZINC SULPHATE) SOLUTION

4.1 Design parameter

Current supplied during electrolysis of spent

165amp.

Maximum flow rate of spent 11 m³/sMinimum flow rate of spent 8 m³/s

4.2 Methodology

Measure the length and depth in which spent(acidic zinc sulphate solution) is flowing using metallic tape measure which is cuboidal in shape.

Calculate area in which spent is flowing. Take small piece of cardboard (approx. 2×2cm) Put that piece of cardboard at rear end. Note the time taken to travel a small piece of cardboard to front end using stop watch. Calculate velocity for each time. Calculate flow rate for each time. Take multiple readings. Calculate mean flow rate of all the readings.

Note

1. Reading was taken on 22nd day after scheduled cleaning and maintenance ( in every 15 days) of spent solution flow rate and cell house in an interval of a hour

https://en.wikipedia.org/wiki/%C3%97

OBSERVATION TABLE NO. 3

Sr no. Length(L)

metre

Depth(D)

metre

Area (A)

Metre square

Time(T)

second

Velocity(V=L/T)Metre per

second

Flow rate (Q=A.V)

Metre cube per second

1 3.26m 1.2m 3.912 1.60 2.43 9.52

2 3.26m 1.2m 3.912 1.60 2.44 9.58

3 3.26m 1.2m 3.912 1.58 2.47 9.69

4 3.26m 1.2m 3.912 1.62 2.41 9.44

5 3.26m 1.2m 3.912 1.61 2.42 9.47Mean flow rate 9.54

CONCLUSION

It was a wonderful and learning experience for me while working on this project. This project took me through the good industrial working experience and while working in maintenance department I have learnt about cooling tower, calculating efficiency of cooling tower, material required , cooling tower fan ,characteristics of fan in industry, calculating flow rate of spent solution and got brief idea of control room functioning.

SCHEDULE

18/5/2015 Safety training

25/5/2015 Cell house area visit, control room area visit

1/6/2015 Project analysis, project related study

8/6/2015 To calculate cooling efficiency of cooling tower

15/6/2015 To calculate velocity of air cooler

22/6/2015 To calculate flow rate of spent

29/6/2015 Project documentation ,project report submission

9/7/2015 Project presentation

REFRENCES Bureau of energy efficiency Manual by host organization Cheresources.com

final report on spent solution in hydro

Engineering