Browsing by Author "Morton A. Barlaz, Co-chair"

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    Development of Models for Calculating the Life Cycle Inventory of Methanol by Liquid Phase and Conventional Production Processes
    (2000-06-26) Vaswani, Sudeep; Morton A. Barlaz, Co-chair; H. Christopher Frey, Co-chair; John H. van Zanten, Member
    This study deals with the development of an ASPEN PLUS process model for the liquid phase methanol (LPMEOH) process,which is in the demonstration phase at Eastman Chemical Company, TN. The model will ultimately be integrated with MSW gasification model being modeled separately and used inan integrated gasification combined cycle (IGCC) system to co-produce methanol and power from syngas obtained from MSWgasification. The LPMEOH process uses syngas as a startingmaterial for methanol production. Model results for anexample case are presented and the life cycle inventory (LCI) of methanol has been calculated starting from syngas. When methanol is produced from the LPMEOH process, its production by conventional processes is avoided. Thus, an EXCEL spreadsheet model of methanol production using conventional process has also been developed. This model calculates the LCI of methanol from conventional process which is used to calculate the emissions avoided per kg ofmethanol produced by the LPMEOH process. For LPMEOH process model, it is found that the performance of the model is dependent on syngas conversion in methanol reactor. Syngas conversion is a function of reactor pressure, syngas space velocity in methanol reactor, molar ratio of recycle gases to fresh syngas feed, and H2/CO molar ratio in syngas feed. The syngas composition mainly depends on the source from which it is obtained (e.g. coal gasification, MSW gasification). LPMEOH process model has the capability to process syngas of varying compositions.Sensitivity analysis of LPMEOH process model has been presented. Based on the sensitivity analysis, it is shown that for syngas compositions limited in hydrogen content, the reactor pressure of or higher than 750 psig must be used. Further it is shown that recycling the unreacted gases has an advantage of more methanol production compared to the case with no recycle. It is also shown that the syngas feed with low H2/CO ratio has lower methanol production than syngas with higher H2/CO ratio. It therefore recommended that the syngas with low H2/CO ratio be adjusted via water-gas shift reaction such that the H2/CO ratio increases thereby resulting in a higher methanol production. It is also learnt that net steam demand in the LPMEOH process increases as the syngas becomes limited in its hydrogen content. This is expected to have some implications when the LPMEOH process is combined with an IGCC system. The LCI of methanol produced by LPMEOH process varies widely with change in syngas composition and process conditions such as reactor pressure, space velocity in methanol reactor, and recycle ratio. The main contribution to the LCI occurs from the combustion of purge gases to produce steam in a boiler. The steam generated offsets the emissions from other contributors of the LCI. The sensitivity analysis of the LCI of methanol production from LPMEOH reveals that the methanol LCI is quite sensitive to the changes in syngas composition, reactor pressure, syngas space velocity and the recycle ratio.The sensitivity analysis of conventional methanol production has also been discussed. It is found that the LCI of conventional process is not very sensitive to changes in natural gas composition, which is used as a raw material for methanol production. The change in syngas conversion in methanol reactor also does not cause the overall LCI of methanol to change significantly.The ultimate objective of the study is to compare the LCI of methanol produced by conventional process with that by LPMEOH process to determine if there is any advantage to methanol production by using LPMEOH technology on syngas derived from MSW gasification. The effect of an LPMEOH process on a gasification system would be an incremental increase in fuel use. Because of the incremental fuel use there would be an increase in elemental sulfur recovered, slag production, and some pollutant emissions. However, an overall LCI of methanol for LPMEOH process would require the calculation of the LCI associated with gasification.