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The Magazine for the World Sulphur and Sulphuric Acid Industries

Sulphur

S P E C I A L C O N F E R E N C E I S S U E

September-October 1998Number 258

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“Solving problemswith bolt-on jackets”“Solving problemswith bolt-on jackets”

Thermal maintenance of moltensulphur is a difficult problem fre-quently faced by engineers in the

sulphur industry. In a refinery, main-taining a temperature window of 280-310°F (138-154°C) is critical (Fig.1).Below 280°F, hydrogen sulphide canbe emitted if vapour space exists, cre-ating a potentially hazardous situation.Above 320°F (160°C) the viscosity ofmolten sulphur rises exponentially.Temperature maintenance problemscan shut down an entire unit or bringa marine terminal’s discharge opera-tions to a standstill. When cross-contamination occurs, the results areusually even more devastating.

These problems are all too wellknown, as are the traditional solu-tions. The sulphur processing andtransport industry has tried severalmethods of maintaining process tem-peratures over the years. Gut lineshave been installed in transfer andtransport piping with some success.However, the risk of cross-contamina-tion associated with gut tracing hasled to alternative means of thermalmaintenance being sought. Tube trac-ing schemes of many varieties havebeen installed on molten sulphur corepiping, pumps, valves and other com-ponents, but with very limited suc-cess. A track record of freeze-ups hasindicated that tube tracing providesinadequate thermal maintenance forsulphur handling. “Blistered pipe” hasbeen generally effective but is quiteexpensive because it is difficult tomanufacture and install.

Fully fabricated, weld-on jack-eted systems have done a good job ofmaintaining molten sulphur temper-atures and are the traditional thermalmaintenance system of choice.

Today, fabricated weld-on jackets

have many loyal adherents who arequick to advocate that approach tothe exclusion of all others.

However, there is another ap-proach to maintaining molten sulphurtemperatures that has proven success-

MOLTEN SULPHUR HANDLING

Sulphur No 258September . October 1998 75

Solving problems withbolt-on jackets

Bolt-on systems have evolved over the past 25 years and are used throughout the molten sulphur processing and sulphur transport industry. H. Gaines of

Controls Southeast, Inc. and P. C. Wielatz of PME Enterprises, Inc. compare bolt-on systems with the traditional fabricated weld-on systems and discuss what to look

for in the design, fabrication and installation of a bolt-on system.

Fig. 1: Viscosity of liquid sulphur

viscosity of liquid sulphur

melting point246°F 119°C

boiling point832°F 445°C

200 300 400 500 600 700 800 900 °F93 149 205 260 316 371 427 483 °C

temperature

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ful in practice. That approach is theinstallation of bolt-on thermal main-tenance technology for both pipe andindividual process components –valves, pumps and instruments.

Bolt-onsBolt-on jackets, in practical terms,match fully fabricated weld-on jacketsat maintaining sulphur between 280°Fand 310°F. They can also provide upto 25% savings in initial investmentcosts versus a fully fabricated system,reduce inventory carrying costs andeliminate the risk of cross-contamina-tion.

Thermally, there is little a fabri-cated system can do in sulphur han-dling that a bolt-on system cannot.The real question should be: Which ismore cost-effective for a particular ap-plication, and is the benefit of margin-ally faster heat recovery after shut-down enough to off-set the risk ofcross-contamination?

This article takes a look at actualservice experience in key areas of ap-plication within sulphur handlingand recovery. It describes the princi-ples of operation for both bolt-onand fabricated weld-on systems. Italso discusses what to look for in thedesign, fabrication and installation ofa bolt-on thermal maintenance sys-tem that can make the difference be-tween a successful operation and aproblematic one.

Note: The phrase “thermal main-tenance” system rather than the usual“process heating” system has beenused because it more accurately rep-resents the system’s true purpose – tomaintain consistent process tempera-ture. Jacketing systems should be eval-uated on their ability to reliably main-tain process temperature levels, nottheir heat-up or recovery capability.Even after a shutdown, it is CSI’s ex-perience that temperature recovery inthe piping is rarely the bottleneck toresuming production.

Case studiesRefinery tail gas service

Bolt-on jackets have been used forover 25 years in tail gas service onvarious components with remarkablesuccess. For example, earlier this year

bolt-on technology solved a tail gasthermal maintenance problem for aFar Eastern petroleum refinery. Therefinery had a 20 inch (51cm) butter-fly valve in tail gas service with aheated stem and disk and a conven-tional weld-on jacket. Because a largeportion of the adjacent flanges, in-cluding the perimeter were exposed,the valve froze regularly. However,since the exposed flanges were cov-ered with ControHeat bolt-on com-ponent jackets six months ago thevalve has been operating without anyproblems.

Sulphur terminal main transfer lineAt the sulphur terminal shown inFigure 2, the 3,500 ft (1067 m) main18inch (46cm) transfer line is heatedwith six ControTrace bolt-on heatingelements. That amounts to approxi-mately four miles of bolt-on trace.

Compared with a fully fabricatedsystem, the processor saved about$100,000 in capital costs (savings ofabout 25%). The line has been oper-ating trouble free for more than twoyears with no freeze-ups and no riskof cross-contamination.

Ship pipingThe M/V Sulphur Enterprise, ownedby Sulphur Carriers, Inc., a subsidiaryof International Shipholding Corpo-ration, was launched in 1994. Shemeasures 524 ft long with a designloaded draft of 33 ft (10m), carrying24,000 tons of molten sulphur (Fig. 3and 4). The ship has 6,300ft (1920m)of ControTrace on more than 1,300ft(396m) of piping. Most of the piperanges in size from 8 inch (20cm) to14 inch (36cm) with heating panels offour and six heating elements. Over30 elbows and ten valves were jack-eted with ControHeat bolt-on jackets.



Fig.2: Approximately four miles of Controls Southeast ControTrace® type bolt-on jacketinghas been installed on this terminal’s main sulphur transfer line.

Fig.3: The M/V Sulphur Enterprise carries 24,000 tons of molten sulphur weekly from Texasand Louisiana to Florida.

Thermal maintenance was specified at278°F (137°C) operating hot oil at amaximum operating temperature of320°F (160°C) and a flow rate of 87gallons/min. Specified insulation was2 inch (5cm) Cal-Sil. Ambient wasspecified to be 20°F (-7°C).

Molten sulphur is loaded at Gal-veston, Texas or Port Sulfur, Loui-siana and transported to Tampa,Florida where it is offloaded at a rateof 2,300 t/h.

When the Sulphur Enterprise wasdesigned, a fully jacketed thermalmaintenance system was specified.However, such a system would havecost 25% more than a comparableControTrace bolt-on system. Achiev-ing equivalent thermal performance ata lower cost was the essential reasonfor selecting bolt-on technology overa fully fabricated system. Another keyconsideration was the elimination of

cross-contamination, a problem thatplagued the Enterprise’s predecessor.

The officers of the Sulphur Enter-prise couldn’t be happier with the de-cision to install a bolt-on system.After four rigorous years at sea, theinsulation surrounding the Contro-Trace and ControHeat remains un-touched. There have been no prob-lems with the lines or componentsthat are maintained thermally by thebolt-on technology.

The conventional fully fabricatedjacketing system

In the traditional thermal mainte-nance approach, a fabricated jacketsurrounds the core pipe or compo-nent with an outer wall. The heatingmedium flows through the annulus

and directly heats the core pipe orcomponent and the process streamwithin. There are many variations ofthe “types” of fully fabricated jack-eted pipe and jacketed componentsavailable. Traditionally, much of thesulphur industry has opted for “stan-dard” jacketed pipe and componentswhich utilize oversize flanges to en-able heat to come in intimate contactwith the flange thereby optimizinguniform temperature distribution(Fig. 5). For valves, this generally re-quires machining off the originalflanges, extending the face-to-face,welding the oversize flanges to thevalve, and then attaching the jacket.

Bolt-on systems for valves,pumps, flow metersBolt-on component jackets are madeto fit closely around valves, pumps andcomponents. These patented heatingjackets are aluminum, cast-to-fitpieces that match the contours of thecomponent to be heated. Embeddedin the casting is a fabricated, pressure-containing chamber through whichflows the heating medium, in the caseof sulphur, water/glycol, steam or hotoil. Heat passes from the mediumthrough the pressure chamber. Thealuminum casting conducts the heatfrom the pressure chamber to sur-round the core components (Figs 6and 7). In this way, the jacket acts as aheat shield under normal operatingconditions (Fig.8). In the event of aprocess upset or other shutdown con-dition, there is enough surface areacoverage to efficiently melt out theprocess and return to normal operat-ing conditions.

Independent pressure boundariesisolate the process stream from theheating medium to eliminate the pos-sibility of cross-contamination. Thistype of bolt-on jacket fits standardvalves, instruments and pumps like aglove with no modification to the orig-inal equipment necessary. Electricallyheated bolt-on jackets are also avail-able.

ControHeat jackets have beenused successfully in more than 50,000applications worldwide in many pro-cess services. With over 4000 patternsfor valves, pumps and meters in in-ventory, most standard process equip-ment can be readily jacketed.



Fig. 4: Bolt-on thermal maintenance systems have operated trouble-free on the SulphurEnterprise since the ship’s launch in 1994.

Fig.5: Spools of jacketed sulphur piping. Note the multiple crosses for rodding out the lines.

Bolt-on systems for pipeBolt-on jackets for pipe are sophisti-cated design refinements of the traceconcept. The heating element is madefrom carbon steel and contoured toexactly mate with the outside diame-ter of the process pipe. The highestquality is made from SA178 Grade Aboiler tubing and pressure tested ac-cording to ASME Code. Heating ele-ments and/or panels are strapped

lengthwise onto the piping and exhibitexcellent heat transfer.

Advantages of bolt-on jacketsThere are two prime reasons for theemergence of the bolt-on alternativein the transport and transfer ofmolten sulphur: lower life cycle own-ership costs and elimination of cross-

contamination risks – both withequal thermal performance.

Equivalent thermal maintenanceperformanceThe temperature window for effec-tively handling molten sulphur is anarrow one. Serious consequences re-sult if sulphur temperatures dropbelow or exceed the operating win-dow. Nevertheless, the fact is that awell designed and properly installedbolt-on system will operate as effec-tively as a fully fabricated system atmaintaining process temperatures be-tween 280 and 310°F.

Advocates for weld-on jacketssometimes argue that fabricated jack-ets transfer heat more efficiently thanbolt-on jackets with their double bar-rier between the heating medium andthe process. That is true. Fabricatedweld-on jackets have a higher heattransfer coefficient. They further as-sert that the difference in heat transferis important for start-ups and recov-ery. However, according to ControlsSoutheast’s experience this is notoften the case. The bottleneck to re-suming production rarely lies in thepipe or individual piping components.Also, with respect to process compo-nents like valves, pumps and instru-ments, it has been observed that thehigher rate of heat transfer is oftenbeing compromised by the amount ofexposed or unheated areas. (Effectivethermal maintenance is a function ofthe heat transfer coefficient, the sur-face area and temperature difference.)For example, if the flanges of the com-ponent or the mating flanges are leftunheated or not adequately heated,they can act as a heat sink, or fin,counteracting the higher “rate of heattransfer”. Or, if the packing area is leftexposed, it can render the equipmentinoperable. Bolt-on jackets for processcomponents enable surface coverageof virtually all of the exposed areasmaking the higher rate of heat trans-fer unimportant.

In the case of bolt-on technologyfor pipe, because the heating elementsare contoured to closely fit the outsidediameter of the pipe, adequate surfacearea contact can be achieved to main-tain specified operating temperatures.Proprietary software modeling capa-bilities are available which specify thenumber of heating elements (surface



Fig.6: These patented heating jackets are aluminum, cast-to-fit pieces that match the con-tours of the components to be heated.

Fig.7: Here Controls Southeast’s ControHeat ® type component jackets heat centrifugal blow-ers used in sulphur recovery at sulphur terminal.

area coverage) required to achievetemperature within a particular win-dow and, if recovery time is a limitingfactor, predict heat-up response.

To illustrate the effectiveness ofControTrace in achieving melt-out,Figure 9 provides the results of a sta-tic heat test performed on a 4 inchschedule 40 carbon steel sulphur lineheated with 2 ControTrace elements.It is important to note that using297°F (147°C) steam, the exposedarea of the pipe wall reached melt-out temperature within 20-30 min-utes.

The equilibrium process temper-ature of 280°F was reached in 2hours and 40 minutes. The limitingfactor to achieving faster melt-out isthe thermal conductivity of the pro-cess itself.

Elimination of cross-contamination risksMix a little sulphur with a little heat-ing medium and there can be bigproblems. Sulphur and steam createsulphurous or sulphuric acid. Sul-phur and hot oil result in quite a lotof mess.

Every maintenance engineer whohas first hand experience with cross-contamination will do virtually any-thing to avoid it from happeningagain. Finding the problems may bemore frustrating than cleaning it upand fixing it. Poor fabrication oftenleads to problems.

Losses can amount quickly – whenoffloading a sulphur ship or barge,losses can easily reach $20,000 per day.If the problem is a run down line in arefinery, they will be even higher. If sul-phur is being transferred to a sulphuricacid plant, the decision whether to in-vestigate bolt-on technology could bebased on losing 1,000 tons of produc-tion per day at say $40/ton, i.e. a dailycost of $40,000.

With bolt-on technology there isno risk of cross-contamination.

Reduce life cycle ownership costsBolt on jackets can also be an advan-tage by lowering the cost of owner-ship. If an application requires ther-mal maintenance of a large number ofpumps, valves, elbows, and instru-mentation, fabricated jacketing willsignificantly raise component replace-ment costs and inventory in order tocontinue production if a problemarises with a component.

Bolt-on jackets, on the other hand,are custom made to fit standard “offthe shelf” components. Consequently,an inventory of customized parts is notrequired. Chances are your local dis-tributor will stock the base componenton which you place the bolt-on jacket.

Further, the initial investmentsavings of ControTrace for pipe ver-sus standard jacketed pipe is between10% and 25%. The difference can beeven greater on large diameter runs.

Quality performancedepends on the sourceIn the final analysis, bolt-on compo-nent jackets and trace jackets willonly be as cost-efficient, reliable andeffective as the designer and installerof the system. The following checklist will help to identify the right ven-dor.● What is the demonstrated exper-

tise of the vendor? What is theirinstalled base in bolt-on thermalmaintenance systems for sulphurtransport and handling? Onlycomprehensive experience willteach them the requirements andfine points they need to know tohelp you to address possible risksand special problems. Ask to seecustomer lists. Check references.Ask for details on bolt-on jobsthat they have done which may besimilar to yours. Ask about designadvice and the heat transfercalculations used to determinewhether adequate surface area is being covered. Ensure that the calculations are run for theworst case scenario (no flow ormelt-out).

● Do they also manufacture fullyfabricated systems? Experiencewith fully fabricated systems en-hances the understanding and ap-preciation for the difference in ca-pability and requirements of thebolt-on technology. In fact, some-times a hybrid system may pro-vide the best solution. For exam-ple, if a sulphur vent line requiresthe system to perform efficientheat exchange duty on the initial50 ft off of the storage unit withthe balance of the line operatingas a true thermal maintenancesystem, the optimum solution is afully fabricated system for the first50ft with ControTrace on the bal-ance of the line.

● Does the vendor ask questions?Encourage them to ask questionsbecause if you hire them, they aregoing to need the answers andsooner is always better than later.There are many process variablesthat help to define the thermalrequirements of a particular ap-plication, for example insulationtype and thickness, process tem-perature, heating medium tem-



Fig.8: The primary function of the bolt-on jacket is to act as a heat shield, compensating forprocess heat loss during normal operation.

perature, ambient design temper-ature and nominal pipe size.

● Does the vendor perform finiteelement modeling, design reviews,thermal profile analysis and tran-sient analysis? Effective modelingwill result in a temperature profileof the piping system at equilibriumand under no flow conditions. Itwill illustrate the heat lost to the at-mosphere through the insulationand the net heat input to theprocess.

● Visit the facilities of the vendoryou have in mind. It provides anexcellent opportunity to deter-mine the extent of their heattransfer and design sophistication.Take along drawings, schematicsand flow plans. Will they reviewthem upon receipt of the purchaseorder or do they simply buildwhat they are asked? Do theymake suggestions? Do they do thedesign work themselves, or dothey subcontract?

● Finally, pay close attention tothe production facilities and

manufacturing operations. Arethey an ASME Code shop? Is thefabrication and inspection pro-cess well documented? Do thecraftsmen have long standing

histories with the company? Isthere daily interaction betweenproduction and engineering? Arerigorous safety policies and pro-cedures adhered to? S



Fig. 9: Static heat test results

Results of a staticheat test performedon a 4 inch schedule40 carbon steel sul-phur line heated withtwo ControTrace typebolt-on elements.Note that using 297°Fsteam the exposedarea of the pipe wallreached melt-outtemperature within 20-30 minutes.Equilibrium processtemperature wasreached in 2 hoursand 40 minutes.

CONTROLS SOUTHEAST, INC.

POST OFFICE BOX 7500

CHARLOTTE, NORTH CAROLINA 28241

TELEPHONE: 704.588.3030

FACSIMILE: 704.588.3039

email: [email protected]

web: www.csiheat.com

Reprinted from British Sulphur, Sept/Oct 1998.British Sulphur, 31 Mount Pleasant,London WC1 0AD, EnglandTelephone: +44 (0) 171 837 5600Fax: +44 (0) 171 8374339Web: http://www.cru-int.com

E N G I N E E R E D S O L U T I O N S F O R H E A T E D P R O C E S S E S

sulphur - inkoinko.com.sg/image/data/catalog/csi/sulphur magazine... · 2018-12-12 · sulphur is a...

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