Implications of process energy efficiency improvements for primary energy consumption and CO2 emissions at the national level

The improvement of energy efficiency is seen as one of the most promising measures for reducing global CO₂ emissions. However, the emission reduction potential may seem different from the industrial plant and policy-maker’s perspectives. This paper evaluates the influences of process heat conservation on CHP electricity production, primary energy consumption and CO₂ emissions from both the mill site and national perspectives. The results indicate that heat conservation in an industrial process may lead to varying results in primary energy consumption and CO₂ emissions, depending on the form of marginal heat production used at the mill site. In the CHP process, reduction of the heat load lowers electricity production, and this reduction may have to be compensated for at the national level. Therefore, the energy conservation potential in industry has to be evaluated by taking into account the connections to the outside society, which means that a wider system boundary than a mill site has to be used. This study demonstrates by theoretical analysis and case mill studies the magnitude of the effects of system boundary definition when evaluating the contribution of an individual energy efficiency investment towards fulfilling the commitment to reduce CO₂ emissions at the national level.     

Testing activity‐based costing to large‐scale combined heat and power plant using bioenergy

This paper deals with the energy production and economics of a large‐scale biomass‐based combined heat and power (CHP) plant. An activity‐based costing model was developed for estimating the production costs of the heat and power of the bio‐CHP. A 100 MW plant (58 MW heat, 29 MW electricity) was used as reference. The production process was divided into four stages: fuel handling, fluidized bed boiler, turbine plant, and flue gas cleaning. The boiler accounted for close to 50% of the production costs. The interest rates and the utilization rate of the CHP had a significant effect on the profitability. We found that below 4000–4500 h per year utilization, the electricity production turned unprofitable. However, the heat production remained profitable with high interest rate (10%) and a low utilization rate (4000 h). The profitability also depended on the type of biomass used. We found that, e.g. with moderate interest rates and high utilization rate of the plant, the bio‐CHP plant could afford wood and Reed canary grass as fuel sources. Copyright © 2013 John Wiley & Sons, Ltd.     

Biomass-Based Combined Heat and Power Systems

This study aims to identify and evaluate the biomass utilization options and evaluate the sustainable biomass production for combined heat and power (CHP) in Turkey. The total biomass energy potential of Turkey is about 32 Mtoe. The amount of usable biomass potential of Turkey is approximately 17 Mtoe. Among the biomass energy sources, fuel wood seems to be one of the most interesting because its share of the total energy production of Turkey is high at 21%. The use of biofuels for CHP on a large scale is focused mainly on forest industry sites, where considerable quantities of biomass are available. Biomass available for energy can be converted to different types of final energy (e.g., electricity, heat), of these, the production of electricity appears to be particularly important. While CHP provides several environmental benefits by making use of waste heat and waste products, air pollution is a concern any time fossil fuels or biomass are burned.     

Exergetic analysis of hydrogen utilisation pathways – Part 1: Energy supply in buildings

This article analyses exergy losses along hydrogen utilisation pathways recently discussed in Germany and other countries. As a renewable fuel hydrogen will be an important part of sustainable future economies. Hydrogen can be used in all sectors, especially in buildings, for mobility and in industry, e.g. in steel production or ammonia synthesis. However, hydrogen has to be produced in a sustainable way. The most promising production is via water electrolysis using renewable electricity. In the first part of this work, exergy analysis is made for the complete hydrogen pathways from production until final utilisation for energy supply in buildings. The second part will focus on pathways for mobility. In the third part, the results are compared with available alternatives to hydrogen such as direct use of electricity in building supply or mobility. The results for building energy supply show that firstly transportation in pipelines (mixture with natural gas and pure hydrogen) is very efficient. Secondly, major exergy losses are caused by the electrolyser. Thirdly, combustion of renewable hydrogen for room heating in common boilers cause the highest exergy losses, but the use of combined heat and power (CHP) units or fuel cells can improve the exergy efficiency substantially.     

Analysis of advanced energy chain typologies

A method for estimating the effectiveness and CO₂ emissions of advanced energy conversion systems from primary to final energy is presented. A traditional condensing power plant for electricity production and a fuel boiler for heat production based on natural gas were used as the reference system. Several potentially better energy chains were analysed including CHP, tri‐generation, heat pumps and efficiency improvements in final energy use. All above solutions could provide clear reductions in primary energy use and emissions, in most cases tens of per cents, but the results are sensitive to operational conditions. In a heat pump system, the primary energy savings are considerable but emission reductions may turn out to be marginal or even negative whereas in co‐generation the emission reductions are higher than energy savings. Striving for high conversion efficiencies would ensure sustained benefits from the advanced energy chain typologies over the reference system even in the less favourable cases. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermo-economics analysis of a cane bio-refinery

A cane bio-refinery consists of the following components: sugar mill, distillery, refinery and cogeneration power plant. The latter supplies electricity and process heat needed by the other components of the bio-refinery. Although process heat and electricity have the same units of energy, they are of different quality levels. Appropriate attention can be directed to those components causing major exergy loss. Furthermore, a device/system can be exergy efficient but may not be cost-effective. Thus, the financial implications need also to be assessed. The performance of an existing cane bio-refinery was assessed on the basis of thermo-economics analysis. It was found that the addition of an evaporator of the falling film thin type in the sugar mill would not only reduce the exergy loss but would also generate more revenues. A better-informed decision could be made for the optimisation of a bio-refinery.     

Comparative analyses of seven technologies to facilitate the integration of fluctuating renewable energy sources

An analysis of seven different technologies is presented. The technologies integrate fluctuating renewable energy sources (RES) such as wind power production into the electricity supply, and the Danish energy system is used as a case. Comprehensive hour-by-hour energy system analyses are conducted of a complete system meeting electricity, heat and transport demands, and including RES, power plants, and combined heat and power production (CHP) for district heating and transport technologies. In conclusion, the most fuel-efficient and least-cost technologies are identified through energy system and feasibility analyses. Large-scale heat pumps prove to be especially promising as they efficiently reduce the production of excess electricity. Flexible electricity demand and electric boilers are low-cost solutions, but their improvement of fuel efficiency is rather limited. Battery electric vehicles constitute the most promising transport integration technology compared with hydrogen fuel cell vehicles (HFCVs). The costs of integrating RES with electrolysers for HFCVs, CHP and micro fuel cell CHP are reduced significantly with more than 50% of RES.     

Value of electric heat boilers and heat pumps for wind power integration

The paper analyses the economic value of using electric heat boilers and heat pumps as wind power integration measures relieving the link between the heat and power production in combined heat and power plants. Both measures have different technical and economic characteristics, making a comparison of the value of these measures relevant. A stochastic, fundamental bottom‐up model, taking the stochastic nature of wind power production explicitly into account when making dispatch decisions, is used to analyse the technical and economical performance of these measures in a North European power system covering Denmark, Finland, Germany, Norway and Sweden. Introduction of heat pumps or electric boilers is beneficial for the integration of wind power, because the curtailment of wind power production is reduced, the price of regulating power is reduced and the number of hours with very low power prices is reduced, making the wind power production more valuable. The system benefits of heat pumps and electric boilers are connected to replacing heat production on fuel oil heat boilers and combined heat and power (CHP) plants using various fuels with heat production using electricity and thereby saving fuel. The benefits of the measures depend highly on the underlying structure of heat production. The integration measures are economical, especially in systems where the marginal heat production costs before the introduction of the heat measures are high, e.g. heat production on heat boilers using fuel oil. Copyright © 2007 John Wiley & Sons, Ltd.     

Decentralized generation of electricity from biomass with proton exchange membrane fuel cell

Biomass can be applied as the primary source for the production of hydrogen in the future. The biomass is converted in an atmospheric fluidized bed gasification process using steam as the gasifying agent. The producer gas needs further cleaning and processing before the hydrogen can be converted in a fuel cell; it is assumed that the gas cleaning processes are able to meet the requirements for a PEM-FC. The compressed hydrogen is supplied to a hydrogen grid and can be used in small-scale decentralized CHP units. In this study it is assumed that the CHP units are based on low temperature PEM fuel cells. For the evaluation of alternative technologies the whole chain of centralized hydrogen production from biomass up to and including decentralized electricity production in PEM fuel cells is considered.Two models for the production of hydrogen from biomass and three models for the combined production of electricity and heat with PEM fuel cells are built using the computer program Cycle-Tempo. Two different levels of hydrogen purity are considered in this evaluation: 60% and 99.99% pure hydrogen. The purity of the hydrogen affects both the efficiencies of the hydrogen production as well as the PEM-FC systems. The electrical exergy efficiency of the PEM-FC system without additional heat production is calculated to be 27.66% in the case of 60% hydrogen and 29.06% in the case of 99.99% pure hydrogen. The electrical exergy efficiencies of the whole conversion chain appear to be 21.68% and 18.74%, respectively. The high losses during purification of the hydrogen gas result in a higher efficiency for the case with low purity hydrogen. The removal of the last impurities strongly increases the overall exergy losses of the conversion chain.     

Techno-economic analysis of using corn stover to supply heat and power to a corn ethanol plant – Part 2: Cost of heat and power generation systems

This paper presents a techno-economic analysis of corn stover fired process heating (PH) and the combined heat and power (CHP) generation systems for a typical corn ethanol plant (ethanol production capacity of 170 dam³). Discounted cash flow method was used to estimate both the capital and operating costs of each system and compared with the existing natural gas fired heating system. Environmental impact assessment of using corn stover, coal and natural gas in the heat and/or power generation systems was also evaluated. Coal fired process heating (PH) system had the lowest annual operating cost due to the low fuel cost, but had the highest environmental and human toxicity impacts. The proposed combined heat and power (CHP) generation system required about 137 Gg of corn stover to generate 9.5 MW of electricity and 52.3 MW of process heat with an overall CHP efficiency of 83.3%. Stover fired CHP system would generate an annual savings of 3.6 M$ with an payback period of 6 y. Economics of the coal fired CHP system was very attractive compared to the stover fired CHP system due to lower fuel cost. But the greenhouse gas emissions per Mg of fuel for the coal fired CHP system was 32 times higher than that of stover fired CHP system. Corn stover fired heat and power generation system for a corn ethanol plant can improve the net energy balance and add environmental benefits to the corn to ethanol biorefinery.     

Energy efficiency analysis and impact evaluation of the application of thermoelectric power cycle to today’s CHP systems

High efficiency thermoelectric generators (TEG) can recover waste heat from both industrial and private sectors. Thus, the development and deployment of TEG may represent one of the main drives for technological change and fuel substitution. This paper will present an analysis of system efficiency related to the integration of TEG into thermal energy systems, especially Combined Heat and Power production (CHP). Representative implementations of installing TEG in CHP plants to utilize waste heat, wherein electricity can be generated in situ as a by-product, will be described to show advantageous configurations for combustion systems. The feasible deployment of TEG in various CHP plants will be examined in terms of heat source temperature range, influences on CHP power specification and thermal environment, as well as potential benefits. The overall conversion efficiency improvements and economic benefits, together with the environmental impact of this deployment, will then be estimated. By using the Danish thermal energy system as a paradigm, this paper will consider the TEG application to district heating systems and power plants through the EnergyPLAN model, which has been created to design suitable energy strategies for the integration of electricity production into the overall energy system.     

Simulation analysis of a repowered double fuel CHP plant including a non‐evaporative heat recovery boiler

A repowering analysis of a conventional, coal‐fired industrial combined heat and power (CHP) plant by means of a gas turbine (GT) and heat recovery boiler (HRB) has been taken into consideration. The existing system, operating in one of the Polish chemical factories consists of coal‐fired boilers, back‐pressure extraction turbines, condensing turbines and steam‐fed district heat exchangers. Two variants of modernization have been proposed and examined from the thermodynamic, environmental protection and economical points of view. The first one includes HRB for preheating the boiler feed water, condensate, and district water, while the steam turbine (ST) system and coal boilers work without any structural changes. The other advanced variant introduces live steam superheaters to HRB. The coal‐fired boilers, in this light, supply only saturated steam (which is introduced into HRB), so they have to be readjusted by replacing the existing superheaters with convective vaporizers for proper flue gas cooling. Such a scheme ensures a considerable reduction of exergy losses in HRB and therefore leads to deeper flue gas cooling and a decrease of coal consumption for the assumed process steam and district heat demands. Heat and process steam demand duration curves for a typical year of operation of the plant have been adapted as input data. The mathematical model of the whole CHP plant has been built on GateCycle and Visual Basic software. The model includes design and off design analyses of boilers, steam and gas turbines and also takes into account shut‐down necessities, concerning machines during their operation outside the acceptable area of their key parameters (e.g. the minimum steam flow in the condensing section of the turbines from the point of view of rotor cooling). The computation was run many times for different sets of input data, read from the demand duration curves. Finally, the yearly values of solid and gaseous fuel consumption, as well as electricity production have been calculated. Both proposed variants of the repowered CHP system have been compared with the existing plant by means of the incremental cumulative economy of chemical energy and pollutant emission. An approximate classical economy analysis net present value (NPV), discounted pay back (DPB) has also been carried out. The whole computation has been replayed for several market GT models. The results obtained lead to the conclusion that repowering of a coal‐fired plant by means of a GT and HRB is a very effective way to improve the thermodynamic and environmental protection aspects of power and heat generation. The introduction of the live steam superheater into HRB provides additional advantages in these fields. The economic results indicate DPBs from 3 to 11 years, depending on the situation at the electricity and fuel markets. Copyright © 2004 John Wiley & Sons, Ltd.     

Black liquor gasification—consequences for both industry and society

The pulp and paper industry consumes large quantities of biofuels to satisfy process requirements. Biomass is however a limited resource, to be used as effectively as possible. Modern pulping operations have excess internal fuels compared to the amounts needed to satisfy process steam demands. The excess fuel is often used for cogeneration of electric power. If market biofuel availability at a reasonable price is limited, import/export to/from a mill however changes the amount of such biofuel available for alternative users. This work compares different mill powerhouse technologies and CHP plant configurations (including conventional recovery boiler technology and black liquor gasification technology) with respect to electric power output from a given fuel resource. Different process steam demand levels for different representative mill types are considered. The comparison accounts for decreased/increased electricity production in an alternative energy system when biofuel is imported/exported to/from the mill. The results show that black liquor gasification is in all cases considered an attractive powerhouse recovery cycle technology. For moderate values of the marginal electric power generation efficiency for biofuel exported to the reference alternative energy system, excess mill internal biofuel should be used on mill site for gas turbine based CHP power generation. The remaining excess biofuels in market pulp mills should be exported and used in the reference alternative energy system in this case. For integrated pulp and paper mills, biofuel should be imported, but only for cogeneration usage (i.e. condensing power units should be avoided). If biofuel can be used elsewhere for high efficiency CHP power generation, mill internal biofuel should be used exclusively for process heating, and the remainder should be exported.     

Assessing the environmental performance and sustainability of bioenergy production in Sweden: A life cycle assessment perspective

Bioenergy is one of the most dynamic and rapidly changing sectors of the global energy economy. The use of food crops for conversion to biofuel has been criticized for several reasons, among which its competition with the global food chain. Instead, lignocellulosic substrates are claimed to provide a bioenergy alternative without competing with food demand. This is particularly true when dealing with residues or waste. In this paper, we explored the environmental performance and sustainability of a bioenergy production system that integrates wastewater treatment, willow farming, and a Combined Heat and Power plant (CHP) located in Enköping (Sweden). Several methodologies for environmental assessment are integrated in this study within a life cycle perspective to investigate material and energy requirements as well as emissions and related impacts of the whole bioenergy production chain. Results show that full integration of different subsystems of a productive network is a desirable option for bioenergy production, within a zero emission oriented production pattern. The investigated wood biomass powered CHP plant was able to co-generate heat and electricity with high production efficiency and much better environmental performance and sustainability than fossil fuel based power plants.     

The effectiveness of storage and relocation options in renewable energy systems

Across the world, energy planners and transmission system operators are faced with decisions on how to deal with challenges associated with high penetration levels of intermittent energy resources and combined heat and power (CHP). At the same time, distributed plant operators are eager to reduce uncertainties related to fuel and electricity price fluctuations. These interests meet-up for options in distributed supply that introduces the principle of storage and relocation, typically by integrating heat pumps (HP) or electric boilers (EBs) into the operational strategies of existing CHP plants. This paper introduces the principle of storage and relocation by energy system design, and proposes for the storage and relocation potential of a technology option to be found by comparing options by their storage and relocation coefficient R_c, defined as the statistical correlation between net electricity exchange between plant and grid, and the electricity demand minus intermittent renewable electricity production. Detailed operational analyses made for various CHP options within the West Danish energy system, point to the concepts of CHP-HP and CHP-HP cold storage for effectively increasing energy system flexibility. For CHP-HP cold storage, R_c increases from 0.518 to 0.547, while the plant's fuel efficiency increases from 92.0% to 97.2%. These findings are discussed within frameworks of renewable energy systems, suggesting principles for 1st, 2nd, and 3rd generation system designs.     

Multi‐objective optimization of a combined heat and power (CHP) system for heating purpose in a paper mill using evolutionary algorithm

The present study deals with a comprehensive thermodynamic modeling of a combined heat and power (CHP) system in a paper mill, which provides 50 MW of electric power and 100 ton h^?1 saturated steam at 13 bars. This CHP plant is composed of air compressor, combustion chamber (CC), Air Preheater, Gas Turbine (GT) and a Heat Recovery Heat Exchanger. The design parameters of this cycle are compressor pressure ratio (r_AC), compressor isentropic efficiency (η_AC), GT isentropic efficiency (η_GT), CC inlet temperature (T₃), and turbine inlet temperature (T₄). In the multi‐objective optimization three objective functions, including CHP exergy efficiency, total cost rate of the system products, and CO₂ emission of the whole plant, are considered. The exergoenvironmental objective function is minimized whereas power plant exergy efficiency is maximized using a Genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost is performed. The results show that at the lower exergetic efficiency, in which the weight of exergoenvironmental objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of the Pareto Frontier with the lower weight of exergoenvironmental objective. In addition, with increasing exergy efficiency, the purchase cost of equipment in the plant is increased as the cost rate of the plant increases. Copyright © 2010 John Wiley & Sons, Ltd.     

Exergoeconomic machine-learning method of integrating a thermochemical Cu–Cl cycle in a multigeneration combined cycle gas turbine for hydrogen production

Integrating new technologies into existing thermal energy systems enables multigenerational production of energy sources with high efficiency. The advantages of multigenerational energy production are reflected in the rapid responsiveness of the adaptation of energy source production to current market conditions. To further increase the useful efficiency of multigeneration energy sources production, we developed an exergoeconomic machine-learning model of the integration of the hydrogen thermochemical Cu–Cl cycle into an existing gas-steam power plant. The hydrogen produced will be stored in tanks and consumed when the market price is favourable. The results of the exergoeconomic machine-learning model show that the production and use of hydrogen, in combination with fuel cells, are expedient for the provision of tertiary services in the electricity system. In the event of a breakdown of the electricity system, hydrogen and fuel cells could be used to produce electricity for use by the thermal power plant. The advantages of own or independent production of electricity are primarily reflected in the start-up of a gas-steam power plant, as it is not possible to start a gas turbine without external electricity. The exergy analysis is also in favour of this, as the integration of the hydrogen thermochemical Cu–Cl cycle into the existing gas-steam power plant increases the exergy efficiency of the process.     

Economic analysis of renewable heat and electricity production by sewage sludge digestion—a case study

In this paper, we assess the total cost of energy recovery from sewage sludge through anaerobic digestion with biogas utilization in combined heat and power (CHP) system. The important advantage of anaerobic digestion process is the production of biogas, which can be used to generate electricity and heat as a source of renewable energy. From this study, it can be retained that the generated thermal energy from the anaerobic digestion process meets the needs of the wastewater treatment plant (WWTP) and guarantees its self‐sufficiency in heat. The surplus of renewable heat produced by CHP is not a primary factor to improve the economic viability of the process. Moreover, the sales of electricity output represent about 76% of the operating costs of anaerobic digestion process. Renewable energy production is not economically viable by its own, without considering the wastewater treatment function and the associated incomes. Nevertheless, sludge digestion helps to reduce the wastewater treatment costs mainly by giving a good source of revenue via electricity production. Copyright © 2014 John Wiley & Sons, Ltd.     

Life cycle energy and environmental analysis of a microgrid power pavilion

Microgrids—generating systems incorporating multiple distributed generator sets linked together to provide local electricity and heat—are one possible alterative to the existing centralized energy system. Potential advantages of microgrids include flexibility in fuel supply options, the ability to limit emissions of greenhouse gases, and energy efficiency improvements through combined heat and power (CHP) applications. As a case study in microgrid performance, this analysis uses a life cycle assessment approach to evaluate the energy and emissions performance of the NextEnergy microgrid Power Pavilion in Detroit, Michigan and a reference conventional system. The microgrid includes generator sets fueled by solar energy, hydrogen, and natural gas. Hydrogen fuel is sourced from both a natural gas steam reforming operation and as a by‐product of a chlorine production operation. The chlorine plant receives electricity exclusively from a hydropower generating station. Results indicate that the use of this microgrid offers a total energy reduction potential of up to 38%, while reductions in non‐renewable energy use could reach 51%. Similarly, emissions of CO₂, a key global warming gas, can be reduced by as much as 60% relative to conventional heat and power systems. Hydrogen fuels are shown to provide a net energy and emissions benefit relative to natural gas only when sourced primarily from the chlorine plant. Copyright © 2006 John Wiley & Sons, Ltd.     

Current state and environmental impact assessment for utilizing oil palm empty fruit bunches for fuel,fiber and fertilizer – A case study of Malaysia

This paper describes the trend of utilizing oil palm residue, i.e. the empty fruit bunches (EFB) left after extraction of the palm oil, using a case study of Malaysia, which is one of the world's major palm oil producers, and discusses the environmental performance of recycling technologies being developed in Malaysia for fuel, fiber, and fertilizer. Seven technologies are analyzed: ethanol production, methane recovery, briquette production, biofuel for combined heat and power (CHP) plants, composting, medium density fiberboard (MDF) production, and pulp and paper production. The life cycle assessment (LCA) method is used to discuss the environmental impacts of these technologies for adding value to this biomass. Sensitivity analyses are conducted to determine the land use effects for the various technologies utilizing EFB and to estimate the energy generation potential of raw EFB in CHP plants and methane production. Among the technologies for energy production, CHP plants have the best performance if the electricity generated is connected to the national grid, with superior benefits in the majority of impact categories compared to briquette, methane, and ethanol production. Overall, we find that methane recovery and composting are more environmentally friendly than other technologies, as measured by reduction of greenhouse gas emissions. Pulp and paper, and MDF production are favorable technologies for land use impacts; however, they have intense primary energy requirements, chemical use in the processes, and emissions from their waste treatment systems. Our results provide information for decision makers when planning for sustainable use of oil palm biomass.