Figure 4 - uploaded by Isabella Greeff
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2 shows the flow sheet of the phthalic anhydride process as simulated in Aspen Plus. The process units of the two energy recovery schemes are also shown and are denoted as belonging to Case A and Case B respectively.
Source publication
Phthalic anhydride (PA) is produced from alkyl-substituted- or multinuclear aromatic compounds such as o-xylene or naphthalene by partial oxidation. With reaction enthalpies as high as -1 793 kJ/mol naphthalene reacted, there are many opportunities for energy recovery making these systems attractive for process integration research.
The production...
Citations
... Expansion of the syngas in a turbine expander is another option to reduce exergy losses, as it allows direct conversion of the heat into work, in stead of downgrading heat to generate steam. The concept of using turbine expanders in chemical processes to recover exothermic reaction heat was investigated extensively by Greeff et al. [6,9e14] and Perold et al. [15]. In this research significant energy savings were realised for a number of well-known chemical processes, namely methanol production, ammonia production, ethylene oxide production, phthalic anhydride and syngas production. ...
Synthesis gas production requires significant amounts of energy. Efficiency improvements and introduction of renewable or non-carbon energy sources are needed to reduce carbon dioxide emissions. Downgrading of high level heat in synthesis gas cooling trains contributes significantly to exergy losses. Recently, turbine expansion of synthesis gas was investigated by various authors, as one method to reduce exergy losses. However, using synthesis gas as a working fluid poses risks to rotating machinery. Thus an externally fired gas power cycle is proposed, which also allows flexibility to incorporate various types of renewable energy sources. In this study helium is the working fluid and nuclear energy the heat source. A helium-steam combined cycle arrangement is simulated and analysed using energy, exergy and cost analysis. Hot synthesis gas is used to provide additional heat to the helium-steam combined cycle via indirect heat exchange, thereby allowing a close match between the temperatures. Further cooling of the synthesis gas via steam generation is also employed. The work output of the integrated system versus a standalone case was increased by at least 19%. The specific exergy destruction in kW/MW work output were reduced by 38% and the specific equipment cost in $/MW work output increased by 22%.
... In the research presented by Greeff et al. significant energy savings was realised for a number of well-known chemical processes, namely methanol production [2], ammonia production [1,3], ethylene oxide production [4] and synthesis gas production [6]. Perold et al. applied the concept to a phthalic anhydride process [7]. Greeff et al. also developed and presented a methodology to lend structure to flow sheet development and analysis of these types of integrated systems [4][5][6]. ...
... Integration of the turbine expander into the conventional flow sheet is based on the methodology for flow sheet development presented in previous work by Greeff et al. [4,6,7]. The flow sheet development is structured around the following criteria: ...
Synthesis gas production provides an excellent opportunity for integration of a turbine expander since the heat is available at very high temperatures (900–1400 °C). This case study considers the integration of a turbine expander with a synthesis gas production process that uses auto-thermal reforming for Fischer-Tropsch synthesis. Auto-thermal reforming technology is a commercialised technology that is well suited to large scale synthesis gas production processes. A methodology that was previously developed and published by the same author is applied in this case study, resulting in an improved flow sheet with significantly improved power output and thermal efficiency improvement. The new flow sheet comprises a unique power production system that uses synthesis gas as a working fluid and wherein the sequence of compression and expansion are reversed in position, compared to conventional power production systems. A conventional steam cycle is also coupled to this synthesis gas power production system to render a combined synthesis gas and steam power production arrangement.
Simulation models were created of the conventional and new integrated flow sheets and the analysis focussed on pressure ratio variations across the turbine expander. It is shown how such variations affect other parameters in the system. In one of the cases a 37% improvement in net work was obtained from the new integrated flow sheet compared to the conventional flow sheet. The results are also compared to the results obtained in a recent study on integration of a turbine expander with a steam methane reformer, and further options to implement the synthesis gas power production system for a steam methane reformer are explored.
... In the research presented by Greeff et al. significant energy savings was realised for a number of well-known chemical processes, namely methanol production [2], ammonia production [1,3], ethylene oxide production [4] and synthesis gas production [6]. Perold et al. applied the concept to a phthalic anhydride process [7]. Greeff et al. also developed and presented a methodology to lend structure to flow sheet development and analysis of these types of integrated systems [4,5,6]. ...
... The dry synthesis gas is heated to the required temperature of the FT reactor. Integration of the turbine expander into the conventional flow sheet is based on the methodology for flow sheet development presented in previous work by Greeff et al. [4,6,7]. The flow sheet development is structured around the following criteria: ...
(Accepted for publication by Applied Thermal Engineering)
Synthesis gas production provides an excellent opportunity for integration of a turbine expander since the heat is available at very high temperatures (900-1400 ˚C). This case study considers the integration of a turbine expander with a synthesis gas production process that uses auto-thermal reforming for Fischer-Tropsch synthesis. Auto-thermal reforming technology is a commercialised technology that is well suited to large scale synthesis gas production processes. A methodology that was previously developed and published by the same author is applied in this case study, resulting in an improved flowsheet with significantly improved power output and thermal efficiency improvement. The new flowsheet comprises a unique power production system that uses synthesis gas as a working fluid and wherein the sequence of compression and expansion are reversed in position, compared to conventional power production systems. A conventional steam cycle is also coupled to this synthesis gas power production system to render a combined synthesis gas and steam power production arrangement.
Simulation models were created of the conventional and new integrated flow sheets and the analysis focussed on pressure ratio variations across the turbine expander. It is shown how such variations affect other parameters in the system. In one of the cases a 37% improvement in net work was obtained from the new integrated flowsheet compared to the conventional flowsheet. The results are also compared to the results obtained in a recent study on integration of a turbine expander with a steam methane reformer, and further options to implement the synthesis gas power production system for a steam methane reformer are explored.
... In another research work [9], a new methodology called energy level composite curves was developed for investigating energy integration of intensive process and its proficiency was probed by exerting it on a methanol case study. Apart from the abovementioned studies in methanol plants, scientists conducted surveys on energetic and exergetic performance of various energy-intensive processes such as ammonia [10,11], phthalic anhydride [12], and synthesis gas generation [13]. This paper is aimed at investigation of an existing methanol plant to recognize the potential of the plant available for energetic and exergetic improvement through incorporation of an expansion gas turbine within the process. ...
... Related to the subject, two theoretical case studies have been developed, namely a study on turbo expander integration in phthalic anhydride production by Perold et al. [9] and a study on methanol production by Greeff et al. [10]. Both these case studies indicated a meaningful scope for energy saving in production of typical chemicals in the integrated processes in comparison with the conventional processes [11]. ...
A techno-economic evaluation for efficient use of energy in a large scale industrial plant of methanol is carried out. This assessment is based on integration of a gas turbine with an existing plant of methanol in which the outlet gas products of exothermic reactor is expanded to power generation. Also, it is decided that methanol production rate is constant through addition of power generation system to the existing methanol plant. Having incorporated a gas turbine with the existing plant, the economic results showed total investment of MUSD 16.9, energy saving of 3.6 MUSD/yr with payback period of approximately 4.7 years.
... The converter produces synthesis gas and functions as the gas turbine combustor. In addition, two conceptual studies have been published; namely, a study on gas turbine integration in phthalic anhydride production [8], and a research on methanol production [9] based on exergy analysis. Both cases studied promising results concerning energy saving and energy efficiency improvement in the production of typical chemicals in the integrated processes in comparison with the conventional processes. ...
This paper is intended to investigate how one can improve the overall energy efficiency of an ammonia process. A gas turbine is integrated with the process to reduce the exergy loss associated with ammonia synthesis loop and produce electricity. Combined Pinch and Exergy Analysis is applied to identify how exergy loss is distributed throughout heat transfer process. This is needed to find appropriate placement for gas turbine integration. Having introduced an exergy loss index for the whole plant, including the heat transfer process and gas turbine system, optimum shaftwork can be generated through recovering part of the exergy loss. Eventually, heat integration of the process streams is done to reduce additional consumption of high pressure steam caused by temperature drop in gas turbine. The results show that 4 MW of electricity can be produced in exchange of adding 7350 kW of high pressure steam. Total amount of exergy loss is reduced by 3323 kW, which indicates 19% reduction compared to the existing process. Based on the economic data, the net income is estimated to be 2,549,653 US$/y with 3 years payback.
... In addition to the patent literature two conceptual case studies on the subject have recently been published, namely a study on turbine expander integration in phthalic anhydride production by Perold et al. (2001) and a study on methanol production by Greeff et al. (2002). Both these case studies showed promising results concerning energy saving in the production of typical chemicals in the integrated processes compared to the conventional processes. ...
... Results of a methanol synthesis case study showed that a 24% energy saving is possible inserting a turbine expander on the methanol reactor outlet (Greeff et al., 2002). In another case study on phthalic anhydride (Perold et al., 2001) it was demonstrated that the amount of power generated is increased from 2.7 MW to 8.1 MW by using a turbine expander on the reaction outlet in combination with the steam turbine cycle that extracts heat from the reactor. ...
This paper investigates the direct integration of a gas turbine power cycle with an ammonia synthesis loop. Such a loop represents a typical reactor–separator system with a recycle stream and cold separation of the product from the recycle loop. The hot reaction products are expanded directly instead of raising steam in a waste heat boiler to drive a steam turbine. Two new combined power and chemicals production flow sheets are developed for the process. The flow sheets are simulated using the flow sheet simulator AspenPlus (licensed by Aspen Technology, Inc.) and compared to a simulated conventional ammonia synthesis loop. The comparison is based on energy as well as exergy analysis. It was found that the pressure ratio over the turbine expander plays an important role in optimisation of an integrated system, specifically due to the process comprising an equilibrium reaction. The inlet temperature to the reactor changes with changing pressure ratio, which in turn determines the conversion and consequently the heat of reaction that is available to produce power. In terms of the minimum work requirement per kg of product a 75% improvement over the conventional process could be obtained. The work penalty due to refrigeration needed for separation was also accounted for. Furthermore this integrated flow sheet also resulted in a decrease in exergy loss and the loss was more evenly distributed between the various unit operations. A detailed exergy analysis over the various unit operations proved to be useful in explaining the overall differences in exergy loss between the flow sheets.
... Direct expansion of reactor product gases to recover reaction heat is a new concept that poses new design challenges. Promising results were already obtained with conceptual studies on turbine expander integration in ammonia synthesis [6,7] as well as phthalic anhydride production [8]. ...
The chemical conversion in a methanol reactor is restricted by equilibrium, therefore the synthesis loop is operated at high pressure and unconverted gas is recycled. Such a synthesis loop consumes large amounts of compression work. In this paper a new flow sheet for methanol synthesis is presented. In this flow sheet the high recycle and operating pressure of the reactor is exploited to produce power. A turbine expander and compressor pair is placed in the recycle stream and utilises the reactor heat at the maximum possible temperature in a process gas power cycle. In conventional systems the reaction heat is often transferred to generate steam to drive steam turbines, but the heat is reduced in quality due to the temperature-driving forces in the heat exchange equipment.Simulation models of the new flow sheet and a conventional flow sheet are created to compare the systems based on energy consumed per kg methanol produced. In the conventional flow sheet the reaction heat is used to generate steam for use in steam turbines. In the new flow sheet a portion of the reaction heat is still transferred to a steam cycle to limit the temperature in the reactor. The remaining heat is used to drive the process gas cycle. The simulation results showed that the new flow sheet consumed overall 24% less energy than the conventional flow sheet.
Synthesis gas is used to produce a wide range of chemicals, e.g. ammonia, methanol or higher hydrocarbons using Fischer-Tropsch synthesis. In the case of coal and natural gas derived synthesis gas such facilities are typically referred to as coal-to-liquids (CTL) or gas-to-liquids (GTL) processes. These processes are implemented on large-scale and require significant amounts of heat and power for internal use, leading to carbon dioxide emissions.
In this work a novel integrated power production process is proposed and investigated. A high temperature gas cooled nuclear reactor is integrated with a synthesis gas production process. The nuclear driven power cycle uses helium as a working fluid. High level heat contained in synthesis gas is directed into the helium cycle, thereby avoiding to a large extent the high temperature driving forces associated with the conventional case of generating steam in waste heat boilers to cool down synthesis gas. The integrated process has the benefit of simultaneously addressing two ways of reducing carbon dioxide emissions, namely efficiency improvement, and substitution of the carbon based heat source with a non-carbon source.
Since only heat energy of synthesis gas is recovered in existing steam methane reforming process, locating a gas turbine at the outlet of reforming furnace is proposed as a new route to have the heat and pressure energy recovered simultaneously. A case with hydrogen yield of 7 x 10(4) Nm(3)h(-1) shows the new gas turbine harvests power of 2262 kW. Questing for more power generation, the integration area is enlarged from the reforming furnace into the total route taking the transfer pressure (P-t) and operating pressure of H-2 purifying PSA device (P-p) as variables. The study demonstrates the new gas turbine harvests the power of 5462 kW when P-t and P-p are stipulated as 3.63 MPa and 1.70 MPa, respectively. Consequently, the total energy consumption and CO2 emission are reduced by 2.5% and 735 gCO(2)/kgH(2), respectively, and the process exergy loss of the synthesis gas is reduced by 5.15% as well.
