Uncertainty in biomass supply estimates: Lessons from a Yakama Nation case study

The increasing demand for bioenergy in the United States necessitates detailed case studies of cost and supply to assess its feasibility. We have developed supply curves based on six feedstocks in five counties surrounding the Yakama Nation in central Washington using spatially explicit estimates of supply and transportation cost. The supply curves were used to examine a base case supply for a bioenergy plant, to analyze the effects of land ownership, and examine the impacts of uncertainty in parameters used to determine cost and supply. The results show that existing industries produce the cheapest supply of feedstock as a byproduct of their operations, while supplies harvested specifically for bioenergy are considerably more expensive. Fragmented land ownerships lead to the necessity of cooperation between owners and highlight the importance of a strong anchor supply close to the plant. Lastly, uncertainty in supply and cost parameters leads to larger ranges in available biomass, leading to reluctant investment in large plants.     

Optimum generation capacities of micro combined heat and power systems in apartment complexes with varying numbers of apartment units

A dynamic simulation of micro combined heat and power (micro-CHP) systems that includes the transient behavior of the system was developed by modeling the generation of electricity and recovery of heat separately. Residential load profiles were calculated based on statistical reports from a Korean government agency, and were used as input data to select the optimum capacities of micro-CHP systems based on the number of apartment units being served, focusing on both economic and energetic criteria. The capacity of internal combustion engine (ICE) based micro-CHP was assumed to be in the range 1–500 kW, and the dependence of the efficiency of the generator unit on the capacity was included. It was found that the configuration (i.e., the capacity and number of generator units) that maximized the annual savings also had favorable energetic performance. Additionally, the statistical mode calculated from the annual electrical load distribution was verified as a suitable indicator when deciding the optimum capacity of a micro-CHP system.     

Optimization of a dual cycle cogeneration system based on a new exergetic performance criterion

An ecological performance analysis for an irreversible dual-cycle cogeneration system has been performed. The objective function is called as the exergetic-performance coefficient (EPC) and defined as the ratio of total exergy output to the loss rate of availability. The general and optimal performances of the irreversible dual-cycle cogeneration system, having a finite-rate of heat transfer, heat leak and internal irreversibilities based on the EPC objective function have been investigated. Comparisons with respect to the optimal total-exergy output are also provided in order to establish the utility of the new exergetic-performance coefficient. The analyzed results of the dual-cycle cogeneration system considered, working at maximum EPC conditions, have a significant advantage in terms of entropy-generation rate and can be used for the selection of optimal design parameters.     

利用螺杆膨胀动力机回收蒸汽余热发电

简述茂名石化利用螺杆膨胀机回收高压聚乙烯装置副产低压蒸汽余热发电工艺,本文介绍了螺杆膨胀机发电的工作原理、结构及技术特点、应用范围、应用方式及经济、节能效益。利用螺杆膨胀机回收蒸汽余热进行发电,发电后产生的凝液达到循环利用,最大程度地提高余热综合利用率。达到节能减排、节电、获得高效益的目的。并认为螺杆膨胀动力机将在石油化工行业有广泛的应用前景。     

Application of evolutionary programming for economic dispatch of cogeneration systems under emission constraints

This paper studies the economical operation of cogeneration systems under emission control with NO_x and SO_x from fossil-fueled thermal generation. The emission model is formulated as a function of fuel enthalpy dependent on the emission factor. The objective function includes fuel cost, emission cost, and tie-line energy cost, subject to the use of mixed fuels, operational limits, and emission constraints. An evolutionary programming was adopted to solve this problem. The steams, fuel mix, and generations will be found by considering the time-of-use dispatch between cogeneration systems and utility companies. A real cogeneration system is given to illustrate the proposed method.     

Conditions for aggregation of CHP plants in the UK electricity market and exploration of plant size

Combined heat and power (CHP) plants with thermal stores may be suitable for sustainable energy production and the accommodation of fluctuating renewable energy sources. At the moment, in the UK, only a few CHP plants have thermal stores. Previous research has shown that thermal stores can improve the economics of CHP plants in the UK under the current market conditions. However, currently, it is only beneficial for CHP plants to sell their electricity to a third party, a Licensed Electricity Supplier, rather than to sell it directly to the power exchange market at prices which are much higher. If CHP plants aggregate, direct access to the power exchange market can become economically viable hence there is the possibility that thermal stores could further improve the economics of CHP plants under an aggregated electricity dispatch. This work firstly explains the conditions under which such plants could aggregate and act as a large power plant in the UK market, and secondly explores the most economic-size of gas engine and thermal store, in the case of aggregation, using energyPRO software and Excel spreadsheets. The work suggests that direct access to the power exchange market can improve the economics of the CHP plants. The highest Net Present Value (NPV), without heat dissipation, for a CHP plant exporting its electricity to the grid for a community heating load of 20 GW h, is more than £5 m, and is obtained for a 6 MW engine with a 28.2 MW h (900 m³) thermal store. The research suggests that such high electricity prices could make even larger plants more profitable than that; however, this can happen only if some of the produced heat is dissipated.     

Optimization analysis of dual-purpose systems

This paper aims to analyze dual-purpose systems focusing the total cost optimization; a superstructure is proposed to present cogeneration systems and desalination technologies alternatives for the synthesis process. The superstructure consists of excluding components, gas turbines or conventional steam generators with excluding alternatives of supplying fuel for each combustion system. Also, backpressure or condensing/extraction steam turbine for supplying process steam could be selected. Finally one desalination unit chosen between electrically-driven or steam-driven reverse osmosis, multi-effect and multistage flash should be included. The analysis herein performed is based on energy and mass conservation equations, as well as the technological limiting equation of equipment. The results for ten different commercial gas turbines revealed that electrically-driven reverse osmosis was always chosen together with both natural gas and gasified biomass gas turbines.     

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.     

Fuel cell micro-CHP techno-economics: Part 2 – Model application to consider the economic and environmental impact of stack degradation

This article presents a literature review regarding the mechanisms of fuel cell degradation, accompanied by the reported range of observed degradation rates in experimental, demonstration and early commercial systems. It then synthesises and exploits this information to investigate the influence of degradation on the economic and environmental credentials of fuel cell micro-combined heat and power (micro-CHP) for the UK residential sector. The investigation applies a techno-economic model developed in the companion article designed to demarcate the key characteristics of commercially successful systems. Two distinct modes of degradation are examined; one proportional to power density in the stack, and the other proportional to thermal-cycling rate of the stack. It is found that limiting the power-density related degradation rate is very important from economic and environmental viewpoints, but thermal-cycling related degradation is less important when thermal energy storage is available because cycling can be avoided. Furthermore it is noted that techno-economic studies that ignore degradation can overestimate the marginal value of a micro-CHP system with respect to the conventional alternative by up to 45% and the CO₂ emissions reduction potential by up to 57%, for performance degradation rates of 2% per MW_eh output. This conclusion is noteworthy because most techno-economic analyses of fuel cells ignore degradation, potentially providing misleading results. Finally it is concluded that existing commercial degradation targets, such as the SECA targets, are appropriate for achieving marketable systems.     

Regulatory mechanism for biomass renewable energy in Brazil,a case study of the Brazilian Babassu oil extraction industry

Brazil has launched the PROINFA program, a regulatory mechanism to incentivize renewable electricity generation. In the light of this new framework, the best economical option for cogeneration was analyzed using one of the biomass resources available in Brazil-Babassu. Thus not only the possible power production but also the potential of such a regulatory tool to enhance the electricity production based on this biomass source, was analyzed. The power production was based on a steam power cycle cogeneration technology within the Babassu palm oil extraction industry in Brazil (Orbignya ssp. (Palmae)). Was used as base for this study: the energetic matrix for the oil extraction plants (for the two main profiles: oil extraction and refining only, and greater vertical integration with the production of other associated products obtained from the Babassu palm oil), utilization of an extraction–condensation turbine, and steam production operating at three levels of temperature and pressure (2.06 MPa/350 °C, 4.56 MPa/420 °C and 6.2 MPa/450 °C). To analyze the economic performance, the framework drawn up by the PROINFA was taken. From the analysis, the best economical/technical option for the design of the cogeneration system was found to be in industrial units with extraction and treatment of crude Babassu oil—steam generation at 4.56 MPa and 420 °C and, for units with a more vertically integrated production scheme—steam generated at 6.2 MPa and 450 °C. As a result, it became clear that the given framework may help the development of new renewable energy sources, but it does not give the necessary threshold to start new projects, neither does it incentive the maximization of the power production for this specific biomass resource.