A Guide to Utilizing Combined Heat and Power in the Wood

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A Guide to Utilizing Combined Heat and Power in the Wood Resources Industry 1 Table of Contents Types of CHP Systems

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A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Table of Contents,Combined Heat and Power CHP Fundamentals 4. Definition and Reasons for Use 4, Understanding System Requirements and Capabilities 5. Load Profiles 5,Operating Strategies 7, Owner Requirements and Additional System Capabilities 9. Types of CHP Systems 11,Thermal Energy Recovery 11. CHP Cycles 12,Topping Cycle 12,Bottoming Cycle 12,Combined Cycle 13.
Overview of Prime Movers 14,Steam Turbines 15,Reciprocating Internal Combustion Engines 15. Combustion Turbines and Microturbines 16,Fuel Cells 18. Stirling Engines 19,Organic Rankine Cycle 19,Summary and Comparison of Prime Movers 20. Woody Biomass Fuels 21,Wood Combustion Calculator 22. Examples of Successful Projects 24,Cox Interior 24.
Rough Ready Lumber 24,Evergreen Community Power Plant 26. List of Affiliates 28,Technical Assistance Programs 28. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Equipment Suppliers 28,Designers 29. Steps for Implementing Design 30,Works Cited 32, 1 The work on which this publication is based was funded in whole or in part through a grant awarded. by the Wood Education and Resource Center Northeastern Area State and Private Forestry and the U S. Forest Service, 2 In accordance with Federal law and U S Department of Agriculture policy this institution is prohibited.
from discriminating on the basis of race color national origin sex or disability. To file a complaint of discrimination write to the USDA Director Office of Civil Rights Room 326 W. Whitten Building 1400 Independence Avenue SW Washington DC 20250 9410 or call 202 720 5964. voice and TDD USDA is an equal opportunity provider and employer. Authors Peter Clarke Dr James Freihaut Bo Lin John Pletcher 12 18 2012. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Executive Summary, A facility owner with an interest or need to increase energy efficiency reduce emissions or increase. energy security should consider using combined heat and power CHP Additionally facilities with. access to on site inexpensive and abundant fuels sources have tremendous potential to fully utilize this. technology Many facilities in the forest products industry fall into this category A CHP system can. economically provide heat and electricity for a facility with a steady source of woody biomass This. guide aims to educate members of the forestry products industry on how to use a source of woody. biomass in a CHP system and provides resources for the development of potential projects In addition. to a thorough overview of CHP concepts this guide also contains technical information for woody. biomass fuels, This guide begins with a general overview of the fundamental principles of CHP systems and highlights. the potential value these CHP systems provide to their host facility Next a discussion of operating. classifications explains how the systems operate on a technical level The general discussion of CHP. systems concludes with a discussion about the characteristics of the most important device in a CHP. system the prime mover This guide includes a discussion of common woody biomass products for. combustion In addition a wood combustion calculator is available for use that determines the. technical combustion potential for woody biomass under specific conditions Three examples of existing. woody biomass CHP projects are also provided to show the versatility and viability of CHP technologies. Finally a contact list for qualified professionals involved with CHP and a guide for project development. is given to support any future efforts of readers to own or operate their own CHP system. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Combined Heat and Power CHP Fundamentals. Definition and Reasons for Use, The majority of facilities use electricity and thermal energy that are derived from separate energy. sources This energy delivery method is known as separate heat and power SHP and is depicted in the. left portion of Figure 1 The fuel utilization efficiency for centralized electric power generation and on. site heat production are 31 and 80 respectively In this case 154 units of fuel would provide 30. units of electricity and 45 units of steam for the end user resulting in an overall efficiency of 49. An alternative approach for meeting the same electricity and thermal requirements is through the use of. combined heat and power CHP also known as cogeneration CHP is defined as the simultaneous. production of electrical or mechanical energy power and useful thermal energy from a single energy. source ASHRAE 2008 This is achieved by recovering heat energy from another process output that. would have otherwise been wasted The CHP method is depicted in the right portion of Figure 1 By. coupling the production of electricity and thermal energy an overall fuel utilization efficiency of 75 is. achievable In other words 100 units of fuel would provide 30 units of electricity and 45 units of steam. for the end user,Figure 1 Comparison of SHP and CHP methods.
Source U S Environmental Protection Agency, A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry, Combined heat and power strategies have been in use for more than 100 years In fact the world s first. electric power plant Thomas Edison s Pearl Street Station New York City 1882 used CHP While only. representing 4 3 of total U S electricity generation in 2010 CHP is a time tested strategy EIA 2011. Understanding System Requirements and Capabilities. Load Profiles, The electric and thermal loads of a facility fluctuate with time Fortunately most of these loads have. predictable frequency and magnitude A load profile curve characterizes a system s use of energy over a. given period of time Figure 2 depicts some of the common characteristics of load profiles over the. course of one day As shown during the early morning and evening hours the load is constant and low. This is called the base load and represents the minimum load at all times In this example the load. demand begins to rise in the morning peaks around mid day and then decreases into the evening The. highest point on the load profile is called the peak load and represents the maximum load at any time. The area between the base load and the peak load is considered the intermediate load. Figure 2 Example daily energy load profile, Not all systems have the same daily load profile as the profile shown in Figure 2 Real systems can. operate in very different ways Figure 3 provides other common daily load profiles for a system. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Figure 3 Various daily load profiles.
In order to consider a facility for its suitability for CHP it is important to understand both the electric. and thermal load profiles Real systems not only have varying load profiles but also often have. independent load profiles for both electricity and thermal energy When considering CHP it is necessary. to contrast the thermal and electric profiles and identify the thermal electric ratio at each point during. the operation of the facility, For many applications in the wood resources industry there is a significant thermal load for wood drying. which can be constant if there are sufficient drying houses with a staggered batch loading strategy This. load will decrease in summer due to higher ambient temperatures and can be combined with space. conditioning requirements in winter such that the winter thermal loads can be several times that of. summer thermal loads This seasonal load profile is generally only relevant to thermal loads as much of. the wood resources industry does not typically employ space cooling. The CHP system can often be sized around this thermal load in a bottoming cycle approach where. steam is generated by a woody biomass fired boiler to meet thermal needs and the steam is passed. through a back pressure turbine generator before being applied to the load In this configuration the. system is often sized to meet the peak thermal needs while the turbine is sized to meet the base. electric needs, When considering topping cycles with natural gas fired prime movers converts fuel to energy engines. turbines gensets the thermal load now becomes more of a limiting factor while the electric output is. still sized to meet the base load In this scenario the CHP system size and type of prime mover should be. selected to meet a thermal and electric load factor of around 80. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Operating Strategies, The feasibility of any CHP system is dependent on the manner in which it would be operated The. required loads of the facility and the size and configuration of major equipment will define the technical. limits of the CHP plant The ultimate operating strategy is determined by the owner s requirements. The first general type of operational strategy is when a CHP plant modulates according to the real time. load demand load following strategy The second strategy is when a CHP plant operates according to. certain triggers such as the amount of load demanded price of fuel time of day or a signal from a. third party conditional strategy It is common to mix these two general strategies into a hybrid control. system Typical operating schemes are described in the following sections and are demonstrated in. Utility Load Conservation, A CHP plant could utilize a conservation strategy when it is more favorable to produce energy on site. than it is to purchase energy from a utility In this arrangement the CHP plant would increase its output. so that on site generation represents a more significant portion of the facility s total load The total load. demand does not change but the facility avoids purchasing high cost or otherwise undesirable energy. from the utility,Utility Load Building, A facility could implement a load building strategy when it is more favorable to purchase energy from a.
utility than it is to produce energy on site Under this arrangement the CHP plant would decrease its. output so that on site generation represents a less significant portion of the facility s total load The. total load demand does not change but the facility can take advantage of purchasing low cost or. otherwise desirable energy from the utility,Base loading. Most facilities have a year round minimum load requirement A base loading operating strategy sets. the CHP plant output for continuous operation at a pre determined base load requirement This. decreases the amount of energy purchased from the utility at all times The CHP plant can provide base. loading for either the electric or thermal load The benefits of the base loading strategy include. predictability of plant operation high plant use factor and reduced dependence on a utility Generally. for successful economic operation the CHP plant should have an annualized electric and thermal load. factor of 80 The annual load factor is the amount of thermal and electric energy used by the building. divided by the system output calculated using 8 760 hours at full load. Peak Load Shaving, Utility companies often require their customers to pay demand charges which are separate from the. charges for quantity of energy consumed These demand charges are based on the customer s. maximum or peak demand over a given period of time typically one month They are determined by. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry, a rate schedule that assigns increased demand charges to customers with a higher maximum demand. Peak demand occurs over a very small fraction of a facility s total operating schedule Considering that. demand charges are paid on every utility bill it is in the best interest of a facility to minimize peak load. requirements, Peak load shaving is an operating strategy that restrains a facility s maximum load required from the. utility This is achieved by setting a CHP plant to load follow once the total load requirement reaches a. pre determined level In effect this caps the amount of energy purchased from the utility at any time. which in turn could reduce the demand charges of that facility. Figure 4 Operating strategies for CHP systems,Utility load conservation Utility load building.
Base loading Peak load shaving,Load demand Utility demand Prime mover output. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry, Owner Requirements and Additional System Capabilities. After understanding the characteristics of the loads demanded and the available control strategies. consideration for the owner s requirements of a CHP system should occur On site CHP technologies are. uniquely positioned to provide valuable services and operational flexibility that are not possible with. separate heat and power strategies However certain tradeoffs associated with CHP systems should be. considered when planning or operating these facilities. Installation Considerations, By definition a CHP system must produce simultaneous heat and power which requires the installation. of purpose built CHP equipment This equipment will require additional space and may produce noise. These constraints can be problematic in densely populated or sensitive areas This additional equipment. will also increase the capital costs of the facility Typically these higher capital costs are justified by a. reasonable return on investment,Operational Considerations. The operating strategies and equipment required of CHP systems is often more complex than an. equivalent SHP system To ensure successful operation the operators of the system need to have a. higher level of technical expertise typically on par with commercial power generation facilities The. larger CHP systems typically rely on specialized outside contractors for all operations maintenance. while the smaller systems can be maintained by in house staff with proper training. Energy and Fuel Systems, Properly designed CHP systems will out perform equivalent SHP systems with regard to primary energy.
use Depending on the choice of fuel this could amount to significant savings in operational fuel costs. Additionally this decrease in primary energy use will yield lower pollutant emissions. An advantage of on site energy systems is the flexibility in fuel choice These types of systems allow for. greater utilization of alternative or opportunity fuels due to proximity to the source Opportunity fuels. are low cost fuels which would otherwise be considered a waste product In the forest products. industry that is sawdust shavings and chips produced on site The use of these types of fuels can help. the host facility reduce its dependence on fossil fuels Although emissions are reduced as a whole in. CHP systems the use of alternative fuels can produce different pollutant emissions Hence a. comprehensive approach should be used for an analysis of the environmental impact of such a system. Reliability and Security, Hospitals data centers and other 24 hour facilities often require uninterrupted or redundant power In. the event of a utility outage an on site CHP system may have the ability to generate power. independently from the grid This standby power configuration could replace the need for. conventional standby generators The traditional standby power approach is usually less cost effective. when compared to a CHP system with standby power capabilities For example a traditional standby. generator will only operate during a grid outage which usually amounts to a few hours out of an entire. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry, year On the other hand a properly sized CHP system could serve a facility s loads near continuously for. an entire year inherently providing standby power The CHP system in this case is providing much more. value to the owner than the traditional standby generator Additionally in the event of a long term. electric grid outage a natural gas fueled CHP system is more reliable and is more likely to retain its fuel. supply than a conventional stand by generator having a finite reserve of liquid fuel. Some facilities have owner requirements or loads which necessitate premium power These. requirements include electricity with high voltage current or enhanced power quality CHP systems are. well suited for these applications because they have the ability to isolate themselves from the. fluctuations in the electric grid output Additionally the local utility distribution network is often fixed. at some intermediate voltage High voltage applications would require the use of a step up transformer. which would entail an efficiency conversion penalty and additional capital costs A CHP system could. generate high voltage from the start and bypass the need for the step up transformers. Additional Revenue Streams, When a CHP system s capacity exceeds the load demand on site the system has the potential to. support the local utility company Utility companies can enter into contracts with CHP facilities so that. when the need arises CHP plants can sell electricity directly to the utility Under this arrangement a. CHP plant will generate excess electricity for sale only at the request of the utility This situation often. arises when there is peak demand on the grid and the utility does not want to operate its own peaking. plants for economic reasons Another situation that may require utility support is when the grid s. capacity is constrained which may occur in urban environments Distributed generators in these areas. have the advantage of producing power near the point of demand relaxing the constraints on the. remaining electricity distribution network, When a CHP system is in close proximity to other energy users and has excess thermal electric capacity. it has the opportunity to sell district energy services This is only possible if the CHP system consistently. has excess capacity district energy distribution infrastructure is available to use and the host facility has. the means to legally sell energy which often requires certification as an Energy Service Company. Depending on the type of fuel used in the CHP plant the host facility could receive tipping charges as a. source of income Tipping charges are fees that are paid for the service of disposing waste In waste to. energy applications it is possible to receive enough tipping charges to cover the collection and. transportation expenses In effect a facility has the potential to have negative fuel costs. Load Shifting, Load shifting is the ability to transfer loads from one time period to another The total facility load over.
a given period of time does not change but the facility load or utility load is manipulated to change the. shape of the load profile This is often achieved through on site generation systems and or thermal. storage strategies The primary motivation for load shifting is to reduce energy costs by consuming less. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry, in high peak periods and or consuming more in off peak periods Load shifting can also help a facility. flatten its load profile so that it can operate with increased stability and or efficiency. Figure 5 Load shifting strategy,Unshifted load demand. Shifted load demand,Types of CHP Systems,Thermal Energy Recovery. The waste heat from a prime mover can be recovered in several ways and used for a variety of. applications The most common practices are direct heating indirect heating and latent heating. Figure 6 Thermal energy recovery methods,Direct heating Indirect heating Latent heating. Input Cold Input Cold Input Liquid, energy Prime fluid energy Prime fluid energy Prime fluid.
mover mover mover,Hot fluid Condenser,Secondary exchanger Secondary. cold fluid Secondary cold fluid Secondary,hot fluid hot fluid. Process Process Process, A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Direct Heating, The working fluid in a direct heating application is typically exhaust gas or coolant fluids from a prime. mover Common direct heating processes include drying processes exhaust fired absorption chillers. desiccant material regeneration in a dehumidifier or supplying a bottoming cycle ASHRAE 2008. Indirect Heating, Two working fluids are present in an indirect heating application The primary working fluid is typically.
exhaust gas or coolant fluids from the prime mover The heat from the primary working fluid is. transferred to a secondary working fluid usually steam or hot water Common indirect heating. processes include generating electric or mechanical power or serving various thermally activated. technologies ASHRAE 2008,Latent Heating, A latent heating application uses two working fluids The primary working fluid is typically exhaust gas. or coolant fluids from the prime mover The heat from the primary working fluid is transferred to a. secondary working fluid The secondary working fluid is selected to change phases in the typical. operating ranges of the process This phase change takes advantage of the latent heat of. evaporation condensation The secondary working fluid is almost always steam ASHRAE 2008. CHP Cycles,Topping Cycle, A topping cycle is an equipment configuration in which the first process is the production of power. Power generation is achieved by applying input energy to a working fluid before it is sent to a prime. mover The mechanical energy from the prime mover is then used to produce power for another. process The waste heat from the prime mover is then sent to a heat recovery device In the heat. recovery device heat flows from the working fluid to supply useful thermal energy for another process. The following is an example of a topping cycle using terminology corresponding to Figure 7 A. combustion turbine prime mover burns natural gas input energy and air working fluid The shaft of. the combustion turbine is coupled to a generator mechanical conversion device to produce electricity. useful energy output The hot exhaust gases from the combustion turbine outlet are ducted to a heat. recovery steam generator heat exchanger to produce steam useful energy output to supply heat for a. drying process,Bottoming Cycle, A bottoming cycle is an equipment configuration in which the last process is the production of power. This is achieved by applying input energy to a working fluid before it is sent to a heat recovery device In. the heat recovery device heat flows from the working fluid to supply useful thermal energy for another. process The remaining thermal energy in the working fluid is then sent to a prime mover The. mechanical energy from the prime mover is then used to produce power for another process. A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry, The following is an example of a bottoming cycle using terminology that corresponds to Figure 7 The. hot exhaust gases primary working fluid from a wood combustion input energy process is ducted to a. heat recovery steam generator heat exchanger to produce steam useful energy output to supply. space heating for a building The excess steam secondary working fluid that is not used for the. separate thermal process is supplied to a steam turbine prime mover This steam turbine is coupled to. a generator mechanical conversion device to produce electricity useful energy output. Combined Cycle, A combined cycle is an equipment configuration in which waste heat from the primary power cycle is.
used to generate additional power In this configuration a prime mover is supplied with input energy. and a working fluid to produce power Waste heat from this process is captured by a heat recovery. device The reclaimed thermal energy is then used by a secondary prime mover to produce additional. A combined cycle can exist in many different configurations An important distinction pertaining to how. power is produced is dependent on whether the cycle is single shaft or multi shaft When both the. primary and secondary prime movers are configured so that their output is directed on the same power. producing device the system is known as a single shaft cycle When the prime movers supply separate. power producing devices the system is known as a multi shaft cycle Another distinction is whether a. combined cycle qualifies as a combined heat and power cycle A common use for the combined cycle is. an electric power plant These plants use the combined cycle to maximize electric power production. not supply separate thermal processes Only combined cycles which simultaneously produce power and. supply thermal energy for a separate process from a single energy source are considered combined heat. and power cycles ASHRAE 2008, The following is an example of a multi shaft CHP combined cycle using terminology that corresponds to. Figure 7 A combustion turbine primary prime mover burns natural gas input energy and air primary. working fluid The shaft of the combustion turbine is coupled to a generator mechanical conversion. device to produce electricity useful energy output The hot exhaust gases from the combustion. turbine outlet are ducted to a heat recovery steam generator heat exchanger to produce steam. secondary working fluid to supply a steam turbine secondary prime mover The shaft of the steam. turbine is coupled to a generator mechanical conversion device to produce additional electricity. useful energy output The steam useful energy output from the steam turbine outlet supplies. heating to the generator in an absorption chiller, A Guide to Utilizing Combined Heat and Power in the Wood. Resources Industry,Figureheat,Combined 7 CHP cyclescycles. and power overview,Topping cycle Bottoming cycle,PM HX HX PM. Fuel or Fuel or,Electricity or Useful Useful Electricity or.
shaft power heat heat shaft power, Multi shaft combined cycle Single shaft combined cycle. MC PM PM MC PM,Electricity or shaft Useful Electricity or Useful. power heat shaft power heat,Input energy Fuel or heat from another process. Working fluid Steam or hot combustion exhaust gases. Mechanical energy Usually the rotation of spinning shaft. Useful energy output Electricity shaft power or heat for another process. PM Prime mover Transforms energy from one form to another turbine engine fuel cell etc. MC Mechanical conversion Converts mechanical energy into power generator pump fan etc. HX Heat exchanger Allows heat to flow between fluids while preventing the fluids from mixing. Overview of Prime Movers, The purpose of the prime mover in a CHP system is to convert fuel or heat energy into mechanical. energy usually shaft power The mechanical energy can power other mechanical equipment such as. fans pumps or compressors or can power a generator to produce electricity The conversion of one.

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