6th International Conference on Chemical Engineering, ICChE 2017

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Thermodynamic assessment of biomass to SNG production considering variable process configurations
MD. IMRAN HOSSAIN, Farzana Jebin, Kawnish Kirtania

Building: Old Academic Building
Room: CHE Seminar Room
Date: 2017-12-22 09:00 AM – 09:15 AM
Last modified: 2018-01-30

Abstract


Thermodynamic assessment of biomass to SNG production considering variable process configurations

Md. Imran Hossain, Farzana Jebin, Kawnish Kirtania*

Department of Chemical Engineering

Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh

both are first authors with equal contribution

*Corresponding Author: kkdwip@che.buet.ac.bd

ABSTRACT

Bangladesh has been experiencing the need for energy resources to generate power in a sustainable way. The installed capacity and maximum generation were 8525 MW and 6350 MW respectively in August 2012 [1], which was the record maximum generation in Bangladesh so far while the actual demand is more than 8000 MW. Generation of electricity in Bangladesh is solely dependent on the availability of conventional sources like indigenous gas, furnace oil, diesel, hydro power and coal. The current total gas reserves of Bangladesh is 16.36 Tcf on the demand for 2.7-3.0 Bcf/d which are set to be exhausted within the next decade, if no new gas fields are discovered[2]. This could potentially lead to the need for other sources of energy, preferably, renewable. Bangladesh has the history of using biomass as household cooking fuels in the remote areas. Converting biomass residues into gaseous fuel (such as synthetic natural gas) could partially solve the energy crisis by supplying the need for household energy uses (i.e. cooking) without affecting the current energy infrastructure.

The main objective of this paper is to conduct thermodynamic assessment of production of synthetic natural gas (SNG) from biomass by using different process configurations. The SNG production process comprises of two major steps: gasification and methanation. Following gasification and gas cleaning, the product gas is cooled and compressed before feeding to water gas shift converter and methanator to produce methane (i.e. SNG). In the last stage, CO2 and H2O are removed from produced SNG.

According to Le Chatelier's principle, for methanation, decreasing temperature increases the conversion for the exothermic reaction while pressure increase favors the reaction forward due to the decrease in the number of molecules. To assess this and different process configurations, the BioSNG production was simulated with four different process configurations using commercial process simulation package ASPEN HYSYS™. In all configurations, outlet stream from the methanator was recycled, and CO2 and H2O were removed from the product stream to produce SNG.

Simulation results showed that the use of only compressor and cooler without any water gas shift converter (WGS) prior to the methanation stage resulted in a methane purity of about ~34% (Case -1). Introducing the WGS after the cooler and compressor contributed to a significant increase in the production of methane. The process configuration using cooler, compressor, water gas shift converter (WGS), an intermediate water and CO2 removal unit after the WGS  showed a methane purity up to ~94% (Case -2). If the water and CO2 removal units were not used after the WGS, the purity of methane reached ~98 % (Case - 3). On the other hand, if only a CO2 removal unit was used after WGS, the purity decreased to ~96 % (Case - 4). Although the purity is slightly lower, the production rate of methane for Case - 3 was found to be the same as Case -4. This lower purity resulted in a slight decrease in the lower heating value (LHV) from 33 MJ/Nm3 (Case - 3) to 32 MJ/Nm3 (Case - 4) for the SNG. Therefore, considering all the configurations, the process without CO2 and water removal (Case - 3) after WGS could be considered as the optimum configuration for BioSNG production with high purity.

REFERENCES

1. A.S.N. Huda, S. Mekhilef, A. Ahsan, 2014, Biomass energy in Bangladesh: Current status and prospects. http:// www.elsevier.com/locate/rser

2. https://www.platts.com/latest-news/natural-gas/dhaka/bangladeshs-existing-gas-reserves-to-run-out-26046254; Accessed on July 30, 2017 at 10 PM

 


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