Manure's allure: Variation of the financial, environmental, and economic benefits from combined heat and power systems integrated with anaerobic digesters at hog farms across geographic and economic regions

Several studies have shown that anaerobic digesters integrated with combined heat and power systems (CHP/AD) are a financially attractive way to generate electricity, reduce odor, and improve nutrient management on hog farms; yet only very few systems have been installed to date. Employing published financial, economic, and environmental indicators, this study tests whether the benefits from CHP/AD identified in these studies can be replicated across all major hog-farming regions in the US. The study finds that a modest support of 1 cent per kWh is needed to assure that CHP/AD generated electricity is competitive with current utility rates in many hog-farming states. However, the study also shows that once CHP/AD systems are promoted hog-farming states stand to reap large benefits from CHP/AD, particularly environmental benefits (such as odor control and emissions reductions), economic benefits (in form of job creation), and added generating capacity.     

CO2 gasification of dairy and swine manure: A life cycle assessment approach

CO₂ gasification of three different chars obtained from the pyrolysis of two dairy manure samples and a swine manure sample was evaluated. Dairy samples were firstly pretreated by anaerobic digestion process and swine sample by bio-drying process. Subsequently, manure samples were pyrolyzed between 30 °C and 980 °C obtaining a solid fuel (biochar), which was later gasified using different vol.% CO₂ (15–90%) which was the gasifying agent. Gasification was conducted at 900 °C. Thermal behavior and gasification characteristics were studied by means of the thermogravimetric-mass spectrometric analysis. In this sense, the reactivity of the samples was influenced by the catalytic activity of the mineral matter contained in the remaining biomass ashes. On the other hand, the viability of the manure gasification process vs the traditional use of manure as fertilizer was studied by means of the life cycle assessment (LCA) methodology. Two different scenarios were analyzed: gasification of manure sample before anaerobic digestion (Pre) and gasification of manure after anaerobic digestion (Dig R). According to the results obtained, the gasification of char Pre was the most viable scenario from the economic and environmental viewpoints whereas the gasification of char Dig R was the best energetic option.     

Life cycle assessment of domestic fuel cell micro combined heat and power generation: Exploring influential factors

Residential Fuel Cell micro combined heat and power (FC-μCHP) systems can help decarburizing the energy system. In the European ene.field project, the environmental performance of FC-μCHP under different conditions was therefore evaluated by means of a comprehensive Life Cycle Assessment (LCA). Important influential factors were explored, i.e. heating demands, full load hours (FLHs) and electricity replacement mixes (ERMs). The systems were compared with a stand-alone Gas Condensing Boiler (GCB) and a heat pump (HP, only in single family homes, SFHs). For the initially assumed FLHs and the current ENTSO-E ERM, relevant environmental impacts including climate change are generally smaller for the FC-μCHPs than for the HP and the stand-alone GCB. In the setting “existing SFHs in central climate” with the highest deployment potential, GHG emission savings are higher the more carbon-intensive the ERM is and/or higher the net electricity export into the grid is. The results are discussed and put into perspective. Further research demands as well as product development opportunities are outlined. The importance of a green hydrogen economy is emphasized.     

Estimating the power and number of microturbines in small-scale combined heat and power systems

Utilizing the combined heat and power (CHP) systems to produce both electricity and heat is growing rapidly due to their high efficiency and low emissions in domestic, commercial, and industrial applications. In the first two categories among available drivers, due to the compact size and low weight, microturbines are attractive choice. In this paper, by using an energy–economic analysis the type and number of the required microturbines for the specific electricity and heat load curves during a year were selected. For performing this task an objective function annual profit (AP) was introduced and maximized. The operation strategy and the payback period of the chosen system was also determined in this study.     

Biomass and bio-energy utilisation in a farm-based combined heat and power facility

Five different renewable energy technologies located at an agricultural and environmental research centre in Northern Ireland, were monitored to assess the cost, performance and efficiency in real-time operation of solar and bio-energy produced from crops and farm wastes utilised for energy generation in industrial grade equipment. Monitoring was conducted over a six year period, with power units running simultaneously or intermittently according to demand from the local district heating system. The purpose of the work was to investigate fossil fuel (oil) displacement, carbon dioxide emission (CO₂e) reductions, financial and environmental sustainability of these technologies in a farm based scenario. Between 2009 and 2014, total heat output from the centre was 7.75 GWh with contributions of 47.2%, 17.1%, 9.8% and 13.5% from the biomass, biogas, multi-fuel boiler and biogas CHP unit respectively. Solar thermal produced 0.49% and the back-up oil boiler 11.9%. Total electrical output was 572.6 MWh with 95.2% generated from biogas CHP and 4.8% from the solar PV system. Fossil fuel and average CO₂e reductions ranged from 20.1% to 54.1% and 23.3–55.7% respectively, reductions that combined with financial savings to present a viable and sustainable renewable energy system.     

Improved load control for a steam cycle combined heat and power plant

The problem of optimum load control of steam power plants has been dealt within many technical papers during the last decades. Deregulation of the power markets and close to the (bio-) fuel source thinking has lead to a trend of small scale combined heat and power plants. These plants are usually operated according to the heat demand and therefore they spend a significant time on partial load. The load control of such plants is in general done by partial arc control. This work applies a hybrid control strategy, which is a combination of partial arc control and sliding pressure control. The method achieves further improvement in performance at partial load. Hybrid control itself is not novel and has earlier been used on traditional coal-fired condensing plants. This has, to the author's knowledge, not earlier been applied on combined heat and power plants. The results show that there is a potential for improved electricity production at a significant part of the load range.     

Supply security for domestic fuels at Finnish combined heat and power plants

The focus of the study was on examining the preparations of Finnish CHP plants for a domestic fuel crisis. National supply security has become topical as the use of domestic fuels, especially peat and wood fuels, has increased over the past decade and temporary regional shortages of domestic fuels have occurred. The study utilised a questionnaire targeting the largest domestic fuel users producing district heating and electricity. The response rate was high, reflecting the importance attached to the subject. The most significant challenges in peat fuel and wood fuel supply security were found to be the time-consuming environmental permit processes for peatlands entering energy use, lack of wood fuel terminals, and the currently unpredictable taxation and subsidy policy. General operation conditions should be improved for domestic fuels' use, and continuity of domestic labour and fuel production must be guaranteed.     

Optimization of a combined heat and power system based gasification of municipal solid waste of Urmia University student dormitories via ANOVA and taguchi approaches

Municipal solid waste (MSW) of Urmia University student dormitories was utilized to trigger a co-generation system. The combined heat and power system consisted of a gasifier, a micro gas turbine, an organic Rankine cycle, a heat exchanger, and a domestic heat recovery. The system performance was validated by comparing the results with experimental results available in the literature. Air, steam, and oxygen were considered as different gasification mediums. Hydrogen content in the case of the steam medium was higher at all gasification temperatures and low moisture contents. However, hydrogen content of the system based oxygen medium was higher at high moisture contents. The system performances from power generation and hot water flow rate viewpoints were assessed versus the MSW flow rate, gasification temperature, pressure ratio, and turbine inlet temperature. Taguchi approach was employed to optimize the generated power in air, steam, and oxygen medium cases. The optimum conditions were the same for all cases. The optimum powers were 281.1 kW, 279.4 kW, and 266.9 kW for the system based steam, air, and oxygen gasifying agents, respectively.     

Exploration of economical sizing of gas engine and thermal store for combined heat and power plants in the UK

There has been discussion about the extent to which combined heat and power (CHP) plants with thermal stores are suitable for sustainable energy production. At the moment, in the UK the development of this type of plant is limited. This paper analyses the economics and optimum size of CHP operating with gas engines and thermal stores in British market conditions. This is achieved using energyPRO software. It is shown that, due to the big differences in electricity prices between day and night, the use of thermal stores could be profitable in the UK. The economical size of CHP plant for a district or community heating load of 20,000 MWh per year is found to be a 3 MWe gas engine with a 7.8 MWh thermal store. In this case the analysis reveals that the use of a thermal store more than doubles the return on investments (as measured in net present value) compared with the same size of a plant without a thermal store. It is concluded that thermal stores can improve the overall economics of CHP plants in present British circumstances.     

A LCA (life cycle assessment) of the methanol production from sugarcane bagasse

Nowadays one of the most important environmental issues is the exponential increase of the greenhouse effect by the polluting action of the industrial and transport sectors. The production of biofuels is considered a viable alternative for the pollution mitigation but also to promote rural development. The work presents an analysis of the environmental impacts of the methanol production from sugarcane bagasse, taking into consideration the balance of the energy life cycle and its net environmental impacts, both are included in a LCA (Life Cycle Assessment) approach. The evaluation is done as a case study of a 100,000 t/y methanol plant, using sugarcane bagasse as raw material. The methanol is produced through the BTL (Biomass to Liquid) route. The results of the environmental impacts were compared to others LCA studies of biofuel and it was showed that there are significant differences of environmental performance among the existing biofuel production system, even for the same feedstock. The differences are dependent on many factors such as farming practices, technology of the biomass conversion. With relation to the result of output/input ratio, the methanol production from sugarcane bagasse showed to be a feasible alternative for the substitution of an amount of fossil methanol obtained from natural gas.     

A life cycle energy assessment for biogas energy in Serbia

The aim of this paper was to present the energy flows in the life cycle of biogas utilization systems (cogeneration and transportation), as well as their mutual relations, starting from providing the feedstock for digestion through to end-of-life management of biogas system as fertilizer on agricultural land. This study was carried out through the energy analysis of two scenarios (biogas in cogeneration and biogas in transportation) using performance of Mirotin biogas plant (1 MW) in Serbia. Results obtained in this study have shown that the analyzed scenario (biogas in cogeneration and biogas in transportation) have positive energy balances (52,114 and 53,585 GJ) and these scenarios are sustainable from energetic point of view.     

A life cycle approach to Green Public Procurement of building materials and elements: A case study on windows

Green Public Procurement (GPP) is a significant policy tool for reducing the environmental impacts of services and products throughout their whole life cycle. Scientific and easily verifiable environmental criteria, based on a life cycle approach, should be developed and used within procurement procedures. In this paper, Life Cycle Assessment (LCA) is applied to wood windows showing how it can support the criteria definition. After a foreword on GPP development in Italy, the evaluation features of the environmental performances of building materials and components are outlined. The LCA case study is then presented, describing the use of the analysis results to define the environmental criteria. LCA allowed to identify the main impacts and the critical processes of the window life cycle, giving a scientific framework to discuss GPP criteria with manufacturers associations and stakeholders. Nevertheless, it couldn’t help neither in identifying detailed criteria for GPP nor to define numerical thresholds to be used as reference in procurement procedures. The appropriate strategies should be selected taking into account the technical status of the market, the standard development and the voluntary industry commitments, involving manufacturers associations. Finally, some elements to develop a structured approach for GPP of construction materials are presented.     

Transient thermal modelling of heat recovery steam generators in combined cycle power plants

Heat recovery steam generator (HRSG) is a major component of a combined cycle power plant (CCPP). This equipment is particularly subject to severe thermal stress especially during cold start‐up period. Hence, it is important to predict the operational parameters of HRSGs such as temperature of steam, water, hot gas and tube metal of heating elements as well as pressure change in drums during transient and steady‐state operation. These parameters may be used for estimating thermal and mechanical stresses which are important in HRSG design and operation. In this paper, the results of a developed thermal model for predicting the working conditions of HRSG elements during transient and steady‐state operations are reported. The model is capable of analysing arbitrary number of pressure levels and any number of elements such as superheater, evaporator, economizer, deaerator, desuperheater, reheater, as well as duct burners. To assess the correct performance of the developed model two kinds of data verification were performed. In the first kind of data verification, the program output was compared with the measured data collected from a cold start‐up of an HRSG at Tehran CCPP. The variations of gas, water/steam and metal temperatures at various sections of HRSG, and pressure in drums were among the studied parameters. Mean differences of about 3.8% for temperature and about 9.2% for pressure were observed in this data comparison. In the second kind of data verification, the steady‐state numerical output of the model was checked with the output of the well‐known commercial software. An average difference of about 1.5% was found between the two latter groups of data. Copyright © 2007 John Wiley & Sons, Ltd.     

垃圾焚烧电厂热电联产的经济性分析

合理利用垃圾资源进行热电联产,是节能减排、改善环境的有力措施。以某2×750 t·d^-1垃圾焚烧电厂为例,通过模型研究发现热电联产可以减少垃圾焚烧电厂的冷源损失,提高全厂热效率;利用一抽蒸汽进行热电联产可实现蒸汽品质的梯级利用,获得较高的经济效益;供热量为30 t·h^-1,垃圾热值由4185.9 kJ·kg^-1增加至8371.7 kJ·kg^-1时,发电量越多,供热能力越强,年热电联产经济效益由7822.76万元增加到14641.07万元;垃圾热值为8371.7 kJ·kg^-1,供热量从10 t·h^-1增加到60 t·h^-1时,垃圾焚烧电厂热效率从28.96%增加到48.50%,年经济效益从13602.74万元增加到15455.66万元。当该地区垃圾热值较高并具备供热条件时,实现垃圾热电联产具有较高的收益。     

Technical and economic assessment of the integrated solar combined cycle power plants in Iran

Thermal efficiency, capacity factor, environmental considerations, investment, fuel and O&M² costs are the main parameters for technical and economic assessment of solar power plants. This analysis has shown that the Integrated Solar Combined Cycle System with 67 MW e solar field (ISCCS-67) is the most suitable plan for the first solar power plant in Iran. The Levelized Energy Costs (LEC) of combined cycle and ISCCS-67 power plants would be equal if 49 million $ of ISCCS-67 capital cost supplied by the international environmental organizations such as Global Environmental Facilities (GEF) and World Bank. This study shows that an ISCCS-67 saves 59 million $ in fuel consumption and reduces about 2.4 million ton in CO₂ emission during 30 years operating period. Increasing of steam turbine capacity by 50%, and 4% improvement in overall efficiency are other advantages of ISCCS-67 power plant. The LEC of ISCCS-67 is 10 and 33% lower than the combined cycle and gas turbine, respectively, at the same capacity factor with consideration of environmental costs.     

Methodology to estimate the economic,emissions, and energy benefits from combined heat and power systems based on system component efficiencies

This paper presents a methodology to estimate the economic, emissions, and energy benefits that could be obtained from a base loaded CHP system using screening parameters and system component efficiencies. On the basis of the location of the system and the facility power to heat ratio, the power that must be supplied by a base loaded CHP system in order to potentially achieve cost, emissions, or primary energy savings can be estimated. A base loaded CHP system is analyzed in nine US cities in different climate zones, which differ in both the local electricity generation fuel mix and local electricity prices. Its potential to produce economic, emissions, and energy savings is quantified on the basis of the minimum fraction of the useful heat to the heat recovered by the CHP system (φ_min). The values for φ_min are determined for each location in terms of cost, emissions, and energy. Results indicate that in terms of cost, four of the nine evaluated cities (Houston, San Francisco, Boulder, and Duluth) do not need to use any of the heat recovered by the CHP system to potentially generate cost savings. On the other hand, in cities such as Seattle, around 86% of the recovered heat needs to be used to potentially provide cost savings. In terms of emissions, only Chicago, Boulder, and Duluth are able to reduce emissions without using any of the recovered heat. In terms of primary energy consumption, only Chicago and Duluth do not require the use of any of the recovered heat to yield primary energy savings. For the rest of the evaluated cities, some of the recovered heat must be used in order to reduce the primary energy consumption with respect to the reference case. In addition, the effect of the efficiency of the power generation unit and the facility power to heat ratio on the potential of the CHP system to reduce cost, emissions, and primary energy is investigated, and a graphical method is presented for examining the trade‐offs between power to heat ratio, base loading fraction, percentage of recovered heat used, and minimum ratios for cost, emissions, and primary energy. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamic modeling and evaluation of solid oxide fuel cell - combined heat and power system operating strategies

Operating strategies of solid oxide fuel cell (SOFC) combined heat and power (CHP) systems are developed and evaluated from a utility, and end-user perspective using a fully integrated SOFC-CHP system dynamic model that resolves the physical states, thermal integration and overall efficiency of the system. The model can be modified for any SOFC-CHP system, but the present analysis is applied to a hotel in southern California based on measured electric and heating loads. Analysis indicates that combined heat and power systems can be operated to benefit both the end-users and the utility, providing more efficient electric generation as well as grid ancillary services, namely dispatchable urban power.Design and operating strategies considered in the paper include optimal sizing of the fuel cell, thermal energy storage to dispatch heat, and operating the fuel cell to provide flexible grid power. Analysis results indicate that with a 13.1% average increase in price-of-electricity (POE), the system can provide the grid with a 50% operating range of dispatchable urban power at an overall thermal efficiency of 80%. This grid-support operating mode increases the operational flexibility of the SOFC-CHP system, which may make the technology an important utility asset for accommodating the increased penetration of intermittent renewable power.     

A critical review of biochemical conversion,sustainability and life cycle assessment of algal biofuels

The increasing global demand of biofuels for energy security and reduction in climate change effects generate the opportunity to explore new biomass sources. Algae is a very promising source of biomass in this context as it sequester a significant quantity of carbon from atmosphere and industrial gases and is also very efficient in utilizing the nutrients from industrial effluents and municipal wastewater. Therefore cultivation of algal biomass provide dual benefit, it provides biomass for the production of biofuels and also save our environment from air and water pollution. The life cycle assessment (LCA) of algal biofuels suggests them to be environmentally better than the fossil fuels but economically it is not yet so attractive.     

A techno-economic analysis of small-scale, biomass-fuelled combined heat and power for community housing

This paper presents the results of a techno-economic study into the feasibility of a number of biomass-fuelled CHP (BCHP) systems when operated in a community housing/mixed use context. Six systems comprising differing technologies have been analysed, with the assumption that the systems operate within an ESCO (energy services company) supply scenario. Actual demand data was obtained for a representative community housing scheme, along with technical performance and cost data on the various biomass CHP systems. Subsequently, an economic modelling tool was developed and a number of operational scenarios were analysed to determine the viability of specific systems and the sensitivity of the results to a range of technical and economic parameters. The impact of thermal storage was also considered in order to optimise heat usage as far as possible. The results indicate that within specific realistic ESCO operating scenarios, biomass CHP can demonstrate positive net present values without the need for capital subsidies. Optimal system design and implementation is critical for profitable operation and it is found that the best economic performance occurs for high load factors when the maximum quantity of both electricity and heat sold on-site is maximised. The results are also found to be very sensitive to a number of the model inputs.     

Ensuring emergency power for critical municipal services with natural gas-fired combined heat and power (CHP) systems: A cost–benefit analysis of a preemptive strategy

Electric power failures in the aftermath of disasters cripple the delivery of critical emergency services. While emergency generators are available in some facilities, these systems are designed for short-term use and support limited functions. The substantial investment required to ensure emergency power for all critical services is difficult to justify because of the uncertainty associated with the likelihood and magnitude of future disasters. Investment evaluations change when a new source of emergency power is considered. This study evaluates the costs and benefits of a program to preemptively install new building-sited electric combined heat and power (CHP) generation technologies to ensure reliable long-term power for critical municipal services in hurricane-prone regions of the US. Three municipalities are selected for this analysis: Houston, Texas; Miami, Florida; and Charleston, South Carolina. Analysis indicates that costs of such a program can, in some cases, provide net energy bill savings regardless of the occurrence of a disaster.