Process Engineering Equipment Handbook Episode 2 Part 4 pdf

Reduced emissions Environmental measures to reduce emissions from the plants are undertaken inresponse to local legislation, license conditions, environmental charges, and taxes,and as v

programs focus on raw material selection and a more precise phosphorus allocation,and the addition of phytase enzyme to improve phosphorus utilization.

Suomen Rehu has been able to reduce the amount of added phosphorus by almost 700 t/a in poultry and pig diets between 1995 and 1997 This enables thereduction of the phosphorus content of manure by 30 percent, which in turnpromotes environmentally compatible livestock production and enables farmers toincrease the number of animals they keep

Feeding management can also be utilized in developing poultry diets without anyadded growth promoter substances with an antibiotic effect; and pork diets withoutany added growth promoters As a result of these types of feeding programs, theproportion of feeds produced by Suomen Rehu without such additives has steadilyincreased In 1997, 85 percent of the pigs fed with Suomen Rehu feeds receiveddiets without any added growth promoters

ISO-VILJATMtechnology, developed by Suomen Rehu, is a commercial quality andenvironmentally oriented cultivation concept Targeted nutritional content andfeeding value, controlled quality with respect to product hygiene and residues, andtraceability from cultivation to transportation and the feed factory are the mostsignificant features of ISO-VILJATMtechnology

ISO-VILJATMis used by Suomen Rehu to enhance the quality of raw materialsused for feed manufacturing A transparent, documented quality chain for animalproduction and livestock-based foodstuffs is employed

The benefits of ISO-VILJATMtechnology to the farmer include better profitability

as a result of higher yields and significant savings in fertilizers In addition,residual nitrogen in the soil can be reduced by up to 60 percent In 1997, 1600farmers adopted this cultivation method, 3000 farmers received training on the

E-46 Environmental Accountability

TABLE E-8 The Most Significant Environmental Incidents at Business Units between 1995 and 1997

CFS Xyrofin, Kotka, Finland A discharge valve of a caustic (NaOH) storage tank was accidentally left open in summer

1996, causing a leak of 22.5 tonnes of caustic soda into the sea A capital project for a new storage tank and distribution system was undertaken as corrective action.

CFS Xyrofin, Kotka, Finland In summer 1997, wastewater was discharged into the sea for seven days (approximately

120 hours in total) due to pretreatment, electricity, and wastewater treatment system failures.

CFS Flavor Technology A package containing ethanol-based flavoring products was shipped improperly from the Corporation, East Windsor, U.S facility in summer 1997 Penalties of FIM 52,000 have been paid This led to changes in

risk management in the shipping of hazardous materials Cultor Baking, Vaasan Baking, An oil leakage took place in summer 1996 as a result of old pipelines and corroded valves Nelo Bakery, Finland The soil was treated immediately in cooperation with the authorities.

Cultor Nutrition Finnsugar, Fire damage in summer 1997 No damage to the environment or production resulted Kantvik, Finland

Cultor Nutrition EWOS, Scotland 1) Land near the factory was previously used for landfill between 1993 and 1996

Landscaping and clean-up was carried out during 1997 Clean-up costs totalled FIM 640,000.

2) Fish oil leakage into a stream took place in summer 1996 A total of FIM 3600 in fines were paid.

3) Fish oil leakage into a stream in late 1996 and early 1997 The case was treated immediately in cooperation with the authorities No legal action was taken.

4) Fuel oil leakage in summer 1997 as a result of the failure of old pipelines Clean-up costs totalled FIM 210,000 A total of FIM 18,000 fines were paid The wastewater system mentioned on Page 29 in this report will reduce the risk of contamination of the local water system from taking place in the future.

 To improve health and safety at bakeries.

Cultor Nutrition

FINNSUGAR DIVISION

 To further reduce the environmental impact of sugar

beet cultivation To incorporate environmental

management in the quality management system.

 To finalize the LCI (Life Cycle Inventory) on sugar beet

and its main products in 1995.

 To further reduce the environmental impact of drying

beet pulp.

 To promote the recovery/recycling of packaging waste

and increase the use of bulk transportation.

 To further improve the division’s environmental

management system and reinforce the image of

Finnish food as clean and wholesome.

implementing the ISO 14001 standard.

 The LCI was completed in 1995.

 The overall nitrogen loading associated with fish feed has been reduced by 80% over the last 20 years, and has now reached the level where further improvements will be difficult to obtain without affecting feed quality properties.

 Work has been done on soya as an alternative protein source.

 Suomen Rehu received ISO 14001 certification in 1996 Value network thinking and supplier auditing have been promoted Improvements have also been made to feeding management systems, and ISO-VILJA TM technology has been introduced.

 Develop Cultor’s environmental database to better meet the needs of both the Group and divisions Improve the reliability of the data collected through the database.

 Develop indicators for environmental, quality, regulatory, and ethical issues to measure performance; and conduct a pilot study to test the suitability of the indicators chosen.

 Implement Cultor’s new Quality and Environmental Policy

in operations.

 Develop documented quality and environmental management systems for all of Cultor’s major business units Divisions to set detailed targets and objectives.

 Continue to conduct LCIs for major products and use LCIs

as an internal environmental management tool.

 Start monitoring transportation data at Group level.

 Improve the follow-up of H&S indicators at both Group and divisional level Develop the data collected and definitions used.

 Start using self-assessment as a Group-wide tool for continuous improvement.

 Continue internal benchmarking for process improvements and start external benchmarking.

 Start divisional cross-auditing.

 Implement the new Regulatory Policy in divisional operations Create standard operational procedures based

on the policy and set goals for Cultor’s regulatory work.

 Implement the Animal Trial Policy in divisional operations.

 Implement the Modern Biotechnology Position Paper in divisional operations.

 Continue proactive dialogue with stakeholders, particularly

in the area of modern biotechnology.

technology, and 14,000 technical leaflets were distributed (See Figs E-39 throughE-41.)

Environmental reports

Objectives and targets. Table E-9 describes the progress that Cultor has made inimplementing the objectives detailed in its 1995 Environmental Report Newobjectives are also given, linked to four key areas: implementation of Cultor’ssustainable development value process, the environment, quality, and regulatoryand ethical issues The objectives and corporate target objectives are updatedannually

E-48 Environmental Accountability

FIG E-39 Taking a chlorophyll measurement on one of the farms using Suomen Rehu’s VILJA TM advanced cereal farming concept (Source: Cultor.)

ISO-Reference and Additional Reading

1 Soares, C M., Environmental Technology and Economics: Sustainable Development in Industry,

FIG E-40 Amount of inorganic phosphorus used at Suomen Rehu (Source: Cultor.)

FIG E-41 Pig feed production with and without growth promoters (Source: Cultor.)

* Source: AssiDomän, Sweden Adapted with permission.

additional costs and revenues generated by environmental measures, whethercompulsory or voluntary A discussion of the term follows with specific reference tothe information source’s corporate policy.

Yardsticks of Environmental Economics (Reference Corporation: AssiDomän)

Biological diversity

External, independent certification of forestry preserves biological diversity at thesame time as active forestry is pursued By means of the certification process, themarket can complement and hasten necessary legislation

The development and introduction of new ecological forestry methods and the certification process are viewed as investments in the future by companies that practice them The additional costs of these efforts within AssiDomän in 1995,

1996, and 1997 have been estimated at MSEK (millions of Swedish kronor) 100,

120, and 150, respectively As the new methods gradually become the acceptednorm, the actual voluntary additional costs are estimated at half this amount.Certification raises the value of forest assets, and certified products are expected

to yield additional revenues amounting to several tens of millions of Swedish kronorfor AssiDomän over many years

These measures contribute strongly to improving global image as a proactive andleading force in the environmental field This is a particularly strong corporateobjective in western European countries, such as Sweden In AssiDomän’s case,much of the corporation’s holdings and the head office are in Sweden However, ithas assets elsewhere, notably Germany

Reduced emissions

Environmental measures to reduce emissions from the plants are undertaken inresponse to local legislation, license conditions, environmental charges, and taxes,and as voluntary investments The Swedish legislation and licensing procedurerequires the best available technology within reasonable economic limits—aneffective stimulus to advances in environmental technology Within AssiDomän,efforts are being concentrated on reducing discharges of oxygen-demandingsubstances to water, reducing emissions of acidifying sulfur and nitrogen oxides toair, and energy conservation measures Large environmental investments are oftenundertaken as part of other major capital investments, particularly at pulp andpaper mills The environmental capital cost is between 10 and 25 percent of theproject (around MSEK 300 in 1997 for AssiDomän) Environmental charges andtaxes amounted to approximately MSEK 50

Note that some of these taxes are specific to individual countries They are not yet globally accepted practice For instance, Sweden charges NOxand SOxtaxes;

as of 2001, the United States does not

Roughly 10–20 percent of the environmental investments can be regarded asvoluntary In some cases they can yield direct additional revenues for products with

an environmental profile (goodwill investment, enhancing the company’s image,name, and trademarks) See also Table E-10

threats of soil acidification and nutrient deficiency in combination with futurewaste requirements and charges Several trials are under way.

 Reduced sulfur content in ship fuels: This voluntary measure incurred a term additional cost for AssiDomän, but was more environmentally cost-effectivethan alternative measures to reduce sulfur emissions It influenced the decision

short-of authorities regarding environmental charges for shipping

Research and development on cleaner and more energy-efficient processes

Research and development investments in the group amounted to around MSEK

210 in 1997 It is estimated that approximately MSEK 65 of these have a direct orindirect link to the environment These investments include the projects concerningbleaching, air and water pollution control, and “ecocycles” that are for the most partbeing pursued on a joint sectoral basis

A unique AssiDomän project in cooperation with suppliers is black liquorgasification, where a demonstration plant is planned at AssiDomän Kraftliner inPiteå This new technology is expected to become a breakthrough that will providehigher energy efficiency and twice the production of electrical energy from biofuel.The project has been granted state energy subsidies amounting to half of theconstruction and experimentation costs totaling MSEK 475

board and sack production

1 Value added is the sum of operating profit after depreciation and payroll expenses.

2 No data available.

3 Energy consumption: source—ÅF-IPK, Energy Consumption in the Pulp

and Paper Industry, 1994 (in Swedish) Value added: source—SCB, Industrial Statistics, 1995.

4 Applies to all plants in the Group.

NOTE : It is AssiDomän’s ambition to contribute to the development of environmental key ratios that can describe how the environmental work affects resource use and financial position Since energy use is strongly environment-related and furthermore an important cost item for the forest products industry, AssiDomän’s energy use is reported here in relation to value added This reflects both the energy intensity of the company’s own activities, and sensitivity to energy price changes.

The difference between 1995 and 1997 is explained for the most part by the fact that the price level for the end products, and thereby the value added, was considerably higher in 1995 It is of interest to note that energy use in relation to value added is nearly 10 times lower in corrugated board and sack manufacture than in the pulp and paper mills The table also shows that AssiDomän is at roughly the same level as the rest of the Swedish pulp and paper industry.

Energy price sensitivity is shown by the fact that when converted to energy costs, the expenditures for electricity and fossil fuels correspond to 10–20 percent of the value added.

Development of resource-efficient packaging

Development of more resource-efficient, lighter-weight, and more transport-efficientpackaging is not just environmentally, but also often economically desirable (SeeFig E-42.) Life-cycle assessments (LCAs)* as a basis for the development work are an important tool here The potential for commercial exploitation of theenvironmental benefits is greater if these benefits can be promoted as part of a newproduct or packaging solution

Examples of such projects within AssiDomän are:

 A stronger sack paper that enables the density of the paper to be reduced by morethan 10 percent for certain applications See Fig E-42

 The launch of the board Frövi Light An example: 25 percent reduced board weightfor a frozen food pack in Germany resulted in fewer and lighter-weight shipmentsplus MSEK 0.7 in reduced packaging charges for the customer

 New barrier-coated papers that replace aluminum-foiled papers, which aredifficult to recycle

 Continued promotion of “eco-white” kraftliner, based on a new process forsignificantly more efficient wood and fiber utilization plus totally chlorine-freebleaching Thanks to the improved environmental profile, it has been possible tospeed up the market introduction, resulting in additional revenues of several tens

of millions of Swedish kronor

Within the corrugated packaging business, a design and material optimizationprogram has been developed and has resulted in the launch of several new types

of packaging with both reduced material consumption and lower costs One example

is a tray for detergent The improved environmental profile convinced the Germanmanufacturer Henkel to choose this new packaging solution, permitting a 28percent weight reduction

Environmental management systems (EMS)

The total costs of work with EMS in the Group during 1997 is estimated to be aboutMSEK 30 EMAS registration or ISO certification provides a strategic advantagefor customer relations, but is not expected to yield direct additional revenues.However, it is noted that setting environmental objectives and plans entailed bycertification/registration can in the long run yield significant efficiency gains thatclearly outweigh the costs See Table E-10

Analysis of potential environmental debts is a part of ongoing EMS work Thecosts of rectifying environmental debts known today are estimated to be less thanMSEK 10

Consequences for Long-Term Profitability

Specific environmental issues in AssiDomän are:

Conservation of the world’s forests

Widespread demands for increased protection of the world’s forests, including growth forest in the northern coniferous forest belt, have led to restrictions andE-52 Environmental Economics

old-* The term life-cycle assessment is used here with a different connotation from that of the entry “LCA,”

which concerns LCA of turbomachinery components.

FIG E-42 Long, strong fibers are a prerequisite for resource-efficient manufacture of strong packaging The photo shows spruce fibers at a magnification of 100 times (Source:

AssiDomän.)

thereby some scarcity of high-quality softwood timber AssiDomän’s vast holdings

of forest land are one of the group’s most important assets in this context, andcertification of these holdings further enhances their value

Emission requirements and environmental charges

Completed environmental investments have given AssiDomän and most otherNordic pulp and paper mills a lead over many international competitors—a leadwhich can often amount to several hundred million Swedish kronor in investmentsper mill In Sweden, environmental charges and taxes on, for example, acidifyingsulfur and nitrogen oxides, as well as on climate-warming carbon dioxide, are used as one of the policy instruments for bringing about environmentalimprovements Such economic instruments are now being adopted to an increasingextent internationally—a trend that will benefit the Swedish forest productsindustry

Legislation concerning packaging, waste paper, and waste

A few years ago, packaging based on new fiber appeared to be seriously threatened

by planned legislation within the EU in particular Waste paper and various wastepaper systems have been favored legislatively The negative consequences have not materialized, however, since the legislation has become less radical andadjustments have been made in the marketplace AssiDomän has increased itsusage of waste paper where this has proved economically and environmentallyfeasible The drive toward increased standardization both in Europe and globallyentails both advantages and disadvantages All things considered, however, thistrend is viewed more as an opportunity than as a threat

Ecolabeling

The ecolabeling of sawn timber is viewed by AssiDomän as economicallyadvantageous since most of AssiDomän’s forestry operations have been FSC-certified There is still very little ecolabeling of packaging, compared with consumer goods Ecolabeling is not expected to affect profitability

Additional Costs, Additional Revenues, and Goodwill

The annual additional costs for environmental investments and otherenvironmental measures that AssiDomän undertakes as strategic, voluntaryinvestments are estimated at MSEK 120–130 The life of these investments canvary widely, however, since the additional values to which they give rise sometimeshave a short duration (environmental promotion, ecolabeling) of one or two years.Forest certification, corporate image, trademarks, and customer alliances areexamples of goodwill investments with considerably longer lives

Industry Comparisons

AssiDomän compares favorably with its Nordic competitors in environmentalconcerns, particularly with regard to forestry practices and the introduction of EMS.The generally high level of environmental compatibility in Nordic companies givesthe Swedish forest product industry a lead over many international competitors in,E-54 Environmental Economics

Reference and Additional Reading

1 Soares, C M., Environmental Technology and Economics: Sustainable Development in Industry,

Butterworth-Heinemann, 1999.

Environmental Ecolabeling*

The purpose of ecolabeling is to distinguish products that have the leastenvironmental impact The criteria for ecolabeling are regularly tightened tostimulate the development of increasingly environmentally sound products.Criteria are based on the total environmental impact of the product throughout itslife cycle Requirements are also made on the function and performance of theproduct

There are several types of ecolabeling, all of which are the object of standardization within the ISO, the International Organization for Standardization.AssiDomän is participating in the Swedish standardization work by offeringviewpoints on the formulation of standards

Within the Nordic Swan ecolabeling system, criteria are developed for packagingpaper and sawn timber products Representatives of AssiDomän are participating

in this work This type of labeling consists of a symbol intended to guide theconsumer in making environmentally informed purchases

Environmental product declaration is another type of ecolabeling where a number

of environmental parameters are declared, but without being evaluated Theprimary target group is large purchasers within industry and government The needfor environmental product declarations has increased with the introduction of EMS,which require environmental information from suppliers and contractors See TableF-4

Environmental Life-Cycle Assessment*

LCA is a method for describing the total environmental impact caused by a product

“from cradle to grave,” i.e., from extraction of the raw materials to final waste disposal See Fig E-43

After the scope of the assessment has been defined, environmental data aregathered from all links in the production chain This phase is called the inventoryand results in a body of data regarding resource and energy use, emissions to airand water, and waste Based on the collected data, an evaluation can then be made

of total environmental impact This is called environmental impact assessment LCA

* Source: AssiDomän, Sweden Adapted with permission.

is used as a guide to the prioritization of remedial measures The method is alsoused in product development for comparing alternative materials from anenvironmental point of view.

Evaporative Coolers (see Chillers; Coolers, Dairy)

Exhaust Stacks (see Stacks)

Exhausters, Centrifugal Gas*

Gas exhausters of the geared type have reduced overall dimensions, weights, andhigh-performance specifications (See Fig E-44.)

Machines of this type are used in geothermal plants where the turbine inlet steamhas a high noncondensable gas content See Table E-10 for a list of example applications

The choice of gas exhauster is dictated both by the noncondensable gas contentand the steam flow rate in the turbogenerator set

This means that installing a centrifugal gas exhauster may prove economicallyadvantageous even for low percentages of gas if the steam flow rate is sufficientlyhigh See Table E-11

The main advantages offered by gas exhausters over alternative solutions areexcellent noncondensable gas extraction process efficiency and the high levels of

E-56 Evaporative Coolers

FIG E-43 Environmental life-cycle assessment (Source: AssiDomän.)

* Source: Ansaldo, Italy Adapted with permission.

vacuum that can be achieved This accounts for power savings of between 40 and

60 percent with respect to other technical solutions such as steam driven ejectors.Centrifugal gas exhausters are designed to offer long term in-service reliability,high performance, and simplicity of design

These design goals have led to the development of centrifugal impellers milledfrom a single piece, or welded together to form a single block, thus improvingresistance to stress and corrosion Advanced three-dimensional wheels are used toachieve efficiency figures close to the values that characterize axial compressors,but with a reduced risk of fouling Particular attention has been given to heatexchange during interstage cooling, achieved by direct contact and dehumidification

of the cooled gas

Expansion Joints*

Expansion joints have been installed on the outlet flange of gas turbine exhaustssince turbines were first used in applications other than to fly planes An expansionjoint is required to isolate the delicately balanced turbine from the thermallyexpanding and vibrating ductwork system

Recent developments in turbine technology have put ever-increasing demands onthe expansion joint supplier to accommodate more and more movements at highertemperatures

Though financial consideration is always a factor, reliability and

trouble-FIG E-44 Compressor set for Castelnuovo geothermal power plant (Italy) (Source: Ansaldo.)

* Source: Townson Expansion Joints, UK.

free service are the ultimate goals of both the end user and expansion joint supplier.

Unfortunately the most competitively priced product does not guarantee thesegoals Expansion joints are an integral part of the exhaust system whose reliability

is every bit as important as the turbine itself If the expansion joint fails then thewhole system must be shut down

Basic Definitions and Configurations

Expansion joint suppliers have individual designs that they have developed andtested over many years These designs may vary from one supplier to another butgenerally there are three basic configurations of expansion joints as seen in Figs.E-45A, E-45B, and E-45C:

 Hot to hot

 Hot to cold

 Cold to coldAlthough designs may vary slightly there are basic principles that must be followed

to ensure a trouble-free life for the expansion joint For example, to avoiddifferential thermal expansion at the connecting flanges, both flanges must be made

E-58 Expansion Joints

TABLE E-11 One OEM’s Sample Applications List—Significant Installations

Customer Plant Country Units Year Fluid Handl Capacity (bar) Ratio (rpm) Drive (1) Acrylonitrile Plant

Tecnimont—Milano 1 1991 Centrifugal 67,000 Nm3/h 0.98 3.34 4,700 4,360

Geothermal Power Station

16,440 Nitric Acid Plant

UHDE-Dortmund for Quimigal 2 1980 Axial-centrifugal 63,400 Nm3/h 0.99 6.06 6,950 5,660

Refinery Service

Mannesmann-Germany for 1 1989 Centrifugal 16,952 kg/h 6.48 1.59 11,252 1,100

Sugar Mill

Sadam S.p.A.—Fermo 1 1988 Centrifugal 116,000 kg/h 2.35 1.41 6,800 2,660

Terephtalic Acid Process

Snam P for Enichem Fibre 1 1986 Gas expander 30,500 Nm3/h 21.50 7,500 2,450 Ottana (Italy)

(1) EM = electric motor (2) End gas = mixture of CO2, H2S, steam.

EMG = electric motor with gear system; GE = gas expander; ST = steam turbine.

SOURCE : Ansaldo.

of the same material and have internal and external insulation designed to allowboth flanges to operate at the same temperature.

Design Principles

Composition

Fabric expansion joints are designed to accommodate the thermal movements andvibration of turbines and adjacent ductwork without imposing any loads on the

FIG E-45A Expansion joint: hot to hot (Source: Townson Expansion Joints.)

FIG E-45B Expansion joint: hot to cold (Source: Townson Expansion Joints.)

FIG E-45C Expansion joint: cold to cold (Source: Townson Expansion Joints.)

turbine outlet flange This is achieved by utilizing a flexible element capable ofwithstanding the high temperature and pressure fluctuations yet able to becompressed or stretched without allowing the exhaust gas to escape.

The composition of a flexible element varies according to the individual supplier’srecommendation but each will contain an impervious gas barrier at some pointwithin the structure This gas barrier is usually made from a layer of PTFE or similiar that would have an operational temperature limitation of around 250°C.The inner layers of the joint are designed to reduce the exhaust gas temperature,which can be as high as 650°C to within the temperature limitations of the gasbarrier

Generally expansion joint flexible elements have a buildup of:

 Outer cover—Weather and mechanical damage barrier

 Gas barrier—Impervious layer of usually PTFE

 Thermal barrier—Layers of fabric or insulation The thickness and composition

of these will depend on the individual supplier and thermal drop required.The flexible element of GT expansion joints should be designed to withstand thefull gas temperature without the aide of an insulation pillow However it is commonpractice to install a full-cavity insulation pillow for the following reasons:

 Prevents fluttering of flexible element

 Reduces noise emission through joint

 Provides additional thermal insulation to expansion joint

Advantages of fabric expansion joints over metallic joints

 Accommodate more thermal movement within a shorter length

 Easy to replace for future maintenance

 Absorb radial growth without damage

 Accommodate lateral movements within a single joint

 Reduce imposed loads on turbine nozzle

Problems and Solutions

Support frame damage

Cracking. Gas turbine exhaust systems are subject to severe temperaturefluctuations ranging from ambient to full exhaust temperature within seconds Thisfeature creates problems for the steel work of the exhaust system and the mountingframe of the expansion joint See Fig E-45A The inside surface of the frame seesthe full gas temperature almost instantly yet the outer flange that the joint ismounted on is at this instant cold This particular frame configuration has beenused successfully for many years on conventional coal-fired stations where there is

a startup period that allows all steel parts to reach optimum gas temperature over

a period of hours rather than seconds

The upstand of the frame in Fig E-45A is designed to position the flexible elementaway from the full gas temperature so that it can survive without burning out.Obviously the higher the upstand the cooler the temperature and the safer the jointbecomes, but in doing this you create greater temperature differentials between thehot inner surface and mounting surface of the expansion joint This is a delicatebalance that is one of the main secrets to a successful expansion joint, keep theE-60 Expansion Joints

joint cold and risk cracking to the frame or keep the frame hot and risk burningthe joint out The cracking of frames is more of a problem in rectangular expansionjoints than circular ones and becomes more of a problem as the size increases.

As a result of the temperature differentials the frame distorts by bowing inward.(See Fig E-46.) The result is flexing of the frames at the corners, which over a shortperiod of time causes cracking Upstands vary depending on the designer but arefrequently seen to be between 100–150 mm, which is sufficient to cause cracking ifprecautions are not taken With finite-element calculations and on-site temperatureexperience we have developed features within the corner design that eliminates thecracking

For example, all welds that are a potential source of cracking have been removed,internal surfaces radiused, and corners stiffened to produce a design that canwithstand several thousand cycles

Distortion. The deflecting of the straight lengths of the expansion joint framecoupled with temperature differentials and induced stresses as a result of weldingcan cause the internal sleeves to distort, which as a result may cause them to clash

or even fall off

The internal sleeves are a vital component for the successful operation of thejoint, the loss of which could result in premature failure of the joint The simplestinternal sleeve design is to weld a flat plate to the side wall of the expansion jointframe See Fig E-45A This is a design that has been operating successfully formany years on conventional coal-fired power plants and smaller GT joints However

as turbines increased in size it became apparent that this basic design needed to

be improved To allow the sleeve to flex with the frame it should be supplied in shortlengths of approximately 1 to 1.5 m with a gap between each piece This gap musthave a cover strip over it to prevent loss of pillow To eliminate distortion as a result

of welding and to stiffen the sleeve, it is suggested that the sleeve be flanged andbolted to the side wall See Fig E-47

Tests and field experience have shown that internal sleeves should not be manufactured too long as this would allow them to vibrate which could cause them to fall off Sleeves over 250 mm must be given special consideration

restraints the number of expansion joints in each system has not increased; it ismerely expected that the same number of joints will accommodate the increasedmovements There comes a time, though, when a simple expansion joint cannotabsorb any more movement individually This is especially true when one considerslateral movements.

Typically at the HRSG inlet the expansion joint sees the vertical growth of theboiler, which can be as much as 150 to 200 mm Inexperienced suppliers would try

to use one single expansion joint for this application but in fact no individual flexibleelement should be asked at these elevated temperatures to absorb more than 60–75-mm lateral movement The materials of the expansion joint start to crease orfold in the vertical side walls as the joint absorbs the lateral movement As the foldsbecome more and more pronounced the external materials of the joint are preventedfrom being cooled by the ambient air, heat builds up, and the joint fails prematurely.The solution to the problem is to simply limit the lateral movement on theindividual joint by:

 Presetting the joint by half the lateral movement

 Installing a double joint with a pantograph control mechanism to equally dividethe movement between both joints See Fig E-48

E-62 Expansion Joints

FIG E-47 Support frame distortion (Source: Townson Expansion Joints.)

FIG E-48 Pantograph design (Source: Townson Expansion Joints.)

Axial movement. Axial thermal movement can create different problems for theexpansion joint than those seen with lateral movements Conventional flat beltexpansion joints when installed have small creases or folds in the corner areas.Under normal operational and small axial movements these creases do not cause

a problem but as movements increase the creases become so pronounced that theoutside materials are not allowed to cool and therefore burn out To prevent thisfrom happening the joint should be constructed with a preformed arch in thecorners See Fig E-49 This configuration will increase the movement capacity ofthe fabric joint to approximately 150 mm; anything above this would require adouble joint using a pantograph mechanism Excessive axial movements can alsoresult in the material of the joint in the straight lengths folding either back on itself

or over the backing bar Either situation would cause premature failure of the joint

Mounting flanges. The flange frame on which the joint is mounted is designed tooperate at very high temperatures as described previously to reduce stress levels.Unfortunately these temperatures frequently cause failure of the expansion joint

if they have not been considered by the expansion joint designer See Fig E-50

FIG.E-49 Flat belt (a) and preformed arch (b) construction (Source: Townson Expansion Joints.)

FIG E-50 Heat damage at mounting flange (Source: Townson Expansion Joints.)

The temperature of the frame is transferred through the mounting bolt to thebacking bar that burns the joint from the outside or allows heat to build up at point

A resulting in premature failure of the joint

Generally at gas temperatures of 400 to 500°C conventional expansion jointsoperate successfully without the need for any special precautions For temperaturesabove these the overall design configuration should be reviewed by finite-elementanalysis to establish the temperature of the backing bars

Should the backing bar temperature be a problem it can be reduced by installing

a gasket under the joint and using thermal barrier washers

Proximity of buildings. Fabric expansion joints are designed to withstand the fullgas temperature but for them to achieve this there must be a relatively cool ambienttemperature of less than 100°C The design of the fabric element is such that thegas temperature is lowered through the different layers of the joint to an acceptablelevel at the point where the gas barrier is located within the joint Frequently jointsare located within the acoustic enclosure where the ambient temperature can behigher than expected, which can result in an abnormal temperature rise throughthe joint and premature failure

High ambient temperatures are a real problem for expansion joint designers.Materials to overcome the problem by providing a gas barrier that will operate atelevated temperatures are limited to the likes of stainless steel foils Unfortunatelyfoils do not absorb movements easily and are prone to cracking from vibration Therecommended way to solve this problem, providing the ambient temperature can-not be reduced, is to blow cooling air over the joint surface The cooler the outsidesurface of the joint the greater the life expectancy Problems of this nature alsooccur when joints located close to buildings or the floor do not allow adequate roomaround the joint for air circulation The closer a structure gets to the outer surface

of the joint the greater the insulating effect it has on the joint surface

Water washing

Expansion joints are designed to withstand hot gases and thermal movements; theyare generally not designed to withstand the moisture that would build up in thejoint from water washing the ductwork or turbine The effect of this is twofold First,the moisture attacks the fiberglass or high temperature fabric layers to a point thatwhen they are dry they will have lost a considerable amount of their tensile strengthand the integrity of the joint will be reduced Second, the water wash often containssolvents to enhance the washing effect These solvents settle in the base of the jointand once the water has vaporized a film remains within the fabrics or on the PTFEgas barrier These solvents have in the past caught fire at startup, which completelydestroys the joint Various materials are available to line the inside face of the joint

to prevent moisture attack, but unfortunately water will eventually get through.The ideal solution to this problem is to prevent the water access to the joint ratherthan trying to accommodate the moisture within the joint See Fig E-51

Radial growth of steel parts

The expansion joint designer has many factors to consider when selecting materials, configurations, and methods of manufacture One condition that is oftenoverlooked is the fact that the steel frame that the joint is mounted on expandsradially at the same rate as it does axially For example a stainless steel frame withinternal duct dimensions of 5 m ¥ 5 m operating at 550°C would expand radially

50 mm, which in effect is stretching the materials of the joint by this amount ToE-64 Expansion Joints

overcome this problem reputable suppliers manufacture the joints using materialscut on a bias (see Fig E-52), which allows the individual layers to stretch by asmuch as 15 percent more than materials cut the conventional way.

Insulation pillows

Pillow loss. Turbine exhaust gases operate at such a high velocity that they cancreate a negative pressure or sucking effect within the expansion joint The jointand steel work are designed to withstand this but the insulation pillows need specialattention The velocity of the gas attacks the very fibers of the pillow and sucksthem downstream in what is known as a picking effect This is a slow process thatgradually works at the pillow until the whole pillow has disappeared There havebeen instances when the pillow as a complete unit has been sucked downstreamthrough the gap in the sleeves To prevent this the pillows must be mechanicallyfixed to either the side wall of the frames or the surface of the sleeves Care must

be taken to allow adequate material between the fixings to accommodate thethermal movement Second, the pillow should be encased in a fine wire mesh toprevent the picking effect High nickel alloy meshes are available that will preventsmall particles passing through Though not always possible due to movementlimitations, utilizing a floating sleeve design (see Fig E-53) helps to overcome thepicking effect

Pillow settlement. Insulation pillows are produced from insulation blankets, which

in turn are manufactured from small strands of either ceramic fiber or fiberglass

FIG E-52 Straight and bias cuts (Source: Townson Expansion Joints.)

Though the density of the material is of the order of more than 150 kg/m, thematerial itself is still quite loose Expansion joints vertically mounted are always

at risk of having the insulation pillows in the vertical legs settle down to the bottom

of the leg exposing the top corners of the joint

Pillows must be manufactured incorporating cushion pins equally spaced acrossthe pillow to keep the layers of insulation bound together In addition pillows should

be either pinned to the side walls or sleeves as described above or flanged so they can be mounted between the expansion joint and mounting steelworks SeeFig E-54

External insulation

Expansion joint manufacturers worldwide insist that the outside of gas turbineexpansion joints must not be insulated over As described previously, covering thejoint would significantly raise the ambient air temperature and cause prematurefailure of the joint The external insulation should be terminated at the joint asshown in Fig E-54 Failure to do this could jeopardize the finite-element calculationthat guarantees the required life cycle of the frames or could cause prematurefailure of the joint as a result of heat buildup from exposure of the steel casing

Noise

Noise requirements must be specified at the inquiry stage as they can significantlyaffect the design of the fabric element and steelwork To achieve optimum noisereduction the joint and pillow must be manufactured from the highest densitymaterial available that will operate at the stated design conditions The internal

E-66 Expansion Joints

FIG E-53 Floating sleeve (Source: Townson Expansion Joints.)

FIG E-54 External insulation (Source: Townson Expansion Joints.)

risking failure of the joint.

In conclusion, nonmetallic expansion joints are the most economical method ofaccommodating thermal expansion in gas turbine and HRSG applications However,

to achieve this the expansion joint supplier must have a proven track record asmost of the above have been developed over many years using finite-elementcalculations, on-site experience, and exposure to problems and providing expansionjoints that have stood the test of time

Explosion; Explosion Hazard Analysis; Explosion Hazards

Explosion hazards are a major consideration in most operating plants Hazardsinclude leaks of flammable liquid and/or a gas One potential culprit is gas-turbinefuel Others may be hydrocarbon product leaks Because of space considerations,analyzing gas-turbine fuel leaks as a hazard will be discussed as a typical case.Although the extracts that follow are from powerplant operators, their methodologywith their gas turbine or combined cycle applications are not restricted to powerproduction applications

Case Study 1: Assessing Explosion Risk Potential at Teesside Power Station, UK*

The potential for an explosion inside a gas turbine combined heat and power (CHP)plant or a combined cycle gas turbine (CCGT) plant enclosure from a fuel leak hasbeen widely addressed in the industry and reviewed at a number of seminars.Enron, the Teesside Power Station operators, contracted a study into the explosionpotential inside the gas turbine (GT) enclosure and to recommend solutions toachieve an acceptable level of risk

A structured approach was applied to identify the hazard, evaluate the risk, andidentify effective, practical, risk reduction measures

The study consisted of:

 A comprehensive air movement study inside the enclosure to define the total airbalance and to create a 3D air velocity grid

 A process hazard review (PHR) to identify credible leak events for the CCGT fuels

 Assessment of the potential for formation of a flammable mixture for each case

 Evaluation of potential ignition sources to review causes and to determine suitable probability values to be used in the risk assessment

* Source: Adapted from extracts from Hunt and Beanland, “A Risk Based Approach to the Potential for CCGT Enclosure Explosions: A Study on Teesside Power Station,” Eutech Engineering Solutions Ltd.,

UK, ASME paper 98-GT-446.

 A hazard analysis (HAZAN) to quantify the risk from an explosion to the operator at most risk.

From the resulting fault trees the most effective options to achieve a measuredreduction in risk were identified These included improved gas detection, aircirculation measures to reduce the incidence of leaks, revised CCGT enclosureaccess, and operating procedures

The structured assessment of the risk and the selection of effective improvements

as applied to the study on Teesside Power Station is covered below

The plant

Teesside Power Station, with a 1875 MW output, is the world’s largest gas-firedcombined cycle heat and powerplant (see Fig E-55) It has a total of eightWestinghouse MW 701 DA gas turbines with associated heat recovery generationand two Westinghouse 800 te/hr steam turbine generators The combinationprovides for low environmental emissions and high thermal efficiency All eightCCGT units are identical having acoustic enclosures for noise suppression withventilation for gas turbine cooling See Table E-12

Figure E-56 shows the station’s basic process flow diagram From this diagram

it can be seen that there are a number of fuel sources available to ensure continuity

of process steam supply to the adjacent chemical companies The primary fuelsource is natural gas supplied from either the Central Area Transmission System(CATS) or Transco’s National Transmission System Backup fuel is available in theform of vaporized propane, which may be used to increase the natural gas Btu value

as a startup fuel prior to introduction of liquid fuel Naphtha is also available foronline transfer to provide security of steam supply in the event of loss of primaryfuel

E-68 Explosion; Explosion Hazard Analysis; Explosion Hazards

FIG E-55 Teesside Power Station (Source: Hunt and Beanland.)

The potential for an explosion from a fuel leak inside gas turbine enclosures forCHP and CCGT plants had been identified, and during early 1996 Enron, theoperator, contracted Eutech to undertake a study into the risk to operators insidethe enclosure from the potential for an explosion from the gas fuel supply.

The study used a structured approach based on experience with carrying outsimilar studies within the chemical/petrochemical industry to identify the hazards,evaluate the risk, and to identify practical risk reduction measures

Unfortunately at 00:25 hr on July 17, 1996, a fire and explosion occurred in CCGT

106 enclosure The incident was due to ignition of a leak of naphtha from a jointduring fuel changeover The explosion injured an operator who had entered the GTenclosure to confirm satisfactory operation of equipment and it caused serious

TABLE E-12 Teesside Power Station CCGT Leak Scenarios

Leak Event Cases Orifice Size (mm) Mass Rates (kg/sec) Mixture Formed

FIG E-56 Teesside Power Station process flow diagram (Source: Hunt and Beanland.)