طراحی مفهومی و تجزیه و تحلیل سیستم یک سیستم چند تولیدی قدرت و تولید الفین از گاز طبیعی

In this paper, a novel poly-generation system for olefin and power production from natural gas is proposed, which integrates hydrocarbon production and the combined cycle power generation. Economic and technological evaluation based on the internal rate of return (IRR) and exergy efficiency is performed. The energy integration results in the proposed poly-generation system for simultaneous production of chemical products (ethylene and propylene) and electricity being more thermodynamically efficient and economically viable than single purpose power generation and chemical products production plants. IRR and exergy efficiency of the proposed poly-generation system are higher than that of natural gas methanol to olefin (NGMTO) system, 18.9% and 49.9%, respectively. The biggest exergy destruction segments, their causes, and possible measures for improvement are investigated simulation and thermodynamic analysis. To analyze the effect of unreacted syngas recycle on the exergy efficiency and economic gains from the proposed poly-generation system, its thermoeconomic optimization model is built by combining economic with thermodynamic analysis. Optimization analysis shows that when 78% of the unreacted syngas is recycled back to the reactor in the methanol synthesization process, the thermoeconomic performance of the poly-generation system is at its optimum.

Industrial energy use is facing dual pressure from access to energy resources and environmental considerations. In some senses, energy shortages and environmental pollution have become critical bottlenecks to sustainable development of the world economy. The development and deployment of integrated energy conversion and chemical systems − poly-generation system − could be a promising approach to meeting increasingly stringent criteria and demand for reliable power supplies. There are many such integrated systems, particularly in chemical and energy industries where processes are flexible and output products could be cascaded and recycled to minimize environmental impacts [1]. Although the investment cost of poly-generation systems is higher, in the long run they are more economical than systems where power, heat and cooling are generated individually [2]. Poly-generation which can achieve the integrated production of energy, petrochemicals, and electricity, has captured the interest of many researchers. Gao investigated a coal-based poly-generation system for power and methanol production using graphical exergy analysis [3]. The results revealed that synthesis on the basis of thermal energy cascade utilization is the main contribution to the performance benefit of a poly-generation system. Kaggerud presented a superstructure block diagram of possible process trains for co-production of energy (electricity) and chemicals products (high purity H2, methanol, urea, and fertilizer). He stated that chemical and process integration gave economy of scale savings, better utilization of raw materials, improved energy efficiency and savings in investment costs [4]. Zhou proposed a co-feed and co-production system based on coal and natural gas for the production of electricity and Dimethyl ether (DME). The analysis results revealed that in terms of economy, energy utilization efficiency and environmental considerations, a Co–Co system is significantly better than single purpose production plant [5]. Wang integrated the traditional acetylene process with the use of fuel cells, and the results of exergy analysis showed that the systematic integration mechanism demonstrably improved the natural gas energy conversion efficiency [6], moreover, flowrate-exergy diagram (FED) was presented to describe the conversion rates of hydrogen and hydrogenous chemicals associating with the exergy loss [7]. Poly-generation, or co-production, has been highlighted in the literature as a promising alternative for the simultaneous production of electricity, hydrogen, synthetic liquid fuels, heat and/or chemicals, [8] and CO2 capture and storage [9]. Using coal gasification, co-production of electricity and C1 chemicals, such as methanol and DME, is currently the focus of poly-generation research [10], [11], [12], [13] and [14]. To our knowledge, however, using natural gas as feedstock, the combined production of power and olefin on integrated plant has still been lack of discussion. Natural gas, as a kind of fossil fuel resource, could play an important role in the future global energy system, particularly if security of supply considerations becomes more pressing. There are abundant natural gas resources in western China, but they are remote from markets or pipe lines. Thus it is a promising option to monetize such “stranded” gas by converting it into easily transported chemical products to bring it to market. With crude oil prices rising sharply and the public’s increasing awareness of environmental issues unremitting efforts are being made to enhance the diversity of energy supply and efficient use of energy. Therefore, it is clearly necessary to develop and deploy integrated technologies to permit the conversion of natural gas into higher quality and more convenient energy carriers or chemical products in an efficient and clean manner with minimal environmental impacts. This paper proposes, as one option to increase the overall efficiency, a novel natural gas-based poly-generation system for olefin and power production with the aim of coupling hydrocarbon production and combined cycle power generation. The main aim is to establish the technical and economic feasibility and thermodynamic performance of the poly-generation system as well as to determine the optimal process parameters. The procedures and results that lead to the evaluation of the performance of the poly-generation system are discussed in detail. First, the concept and technology of the poly-generation system are illustrated in Section 2. Then it is explained how to set up modular flowsheet and simulate the whole system to get the simulation results for the following analysis. Section 4 presents a detailed analysis of the poly-generation system in terms of economic and exergy performance. In Section 5, a thermoeconomic optimization model for integrating the assessment of the economical and exergy performance is built. Based on the above analysis, an evaluation and conclusions are presented.

A novel poly-generation system of natural gas to co-produce electricity and olefin is proposed. Thermodynamics and economic analysis were carried out on the proposed poly-generation system. The results indicate that the proposed poly-generation system for simultaneous production of chemical products (ethylene and propylene) and electricity is more thermodynamically efficient and economically viable than single purpose power generation and chemical products plants. From the exergy loss point of view, exergy destruction occurs mainly in the gasification process and the power plant, which account for 36.4% and 42.1% of the whole exergy loss of the system, respectively. Physical exergy destruction in heat transfer and chemical exergy destruction in the combustion process are the main reasons for the exergy loss of the poly-generation system. Thermoeconomic analysis, which evaluates the energy utilization and economic benefits, is an important and valid approach. A thermoeconomic optimization model of the poly-generation system is built, and the optimal F value, 0.78, is obtained. Although the production of olefin and the exergy efficiency increase with the increase of F; the overall performance of the poly-generation system decreases significantly when F exceeds 0.85. One of the principle advantages of the proposed scheme is flexible to accommodate changes in demand between electricity and oil product market. Another advantage is that natural gas poly-generation is a promising alternative to reduce dependence on oil. Thus, electricity and olefin from natural gas poly-generation can help to develop and deploy integrated technologies to permit high utility efficiency of natural gas into higher quality energy carrier and chemicals.