Application of Low Pressure Water Scrubbing Technique for Increasing Methane Content in Biogas

Abstract

For many developing nations, biogas has traditionally been used for household cooking and lighting. Methane (CH 4) content in biogas has to be increased by removing incombustible carbon dioxide (CO 2) and potentially corrosive constituents such as hydrogen sulphide (H 2 S) and moisture. This study set out to increase biogas from 55.8% CH 4 , 43% CO 2 , 0.85% oxygen (O 2), 75.1 ppm H 2 S to >80% methane and non-traceable H 2 S without enhancing raw biogas pressure. By using a single scrubber column and varying water scrubbing system operating parameters of packing material type, packing depth, water and gas flow rates, appropriate parameters for achieving the above objective were determined. The experiments were carried out at an average digester pressure of 1.0589bar. Results show that packing a column with steel-wire mesh to a depth of 0.4m increases the volumetric percentage of CH 4 in biogas to >80% for water to gas flow rate ratios 1.9 and above. Increasing the packed depth to 0.8m increases volumetric percentage of CH 4 in biogas to 80% at a lower ratio of 0.7. This increase in packed depth resulted in an improvement from 1800 litres to 700 litres of water for every m 3 of raw biogas upgraded. However, to achieve >80% CH 4 in marble packed columns of similar depths, the water to gas flow rate ratio has to be raised above 2.5.

Optimization and Analysis of a Low-Pressure Water Scrubbing Biogas Upgrading System via the Taguchi and Response Surface Methodology Approaches

“…The highest removal efficiency of carbon dioxide of 73.7 percent was obtained at an L/G ratio corresponding to 0.371. However, this ratio seemed abnormally low compared to similar studies corresponding to 2 (Walozi et al, 2016), 1.5 -2.0 (Noorain et al, 2019). The reason for this deviation is likely attributed to the packing material used in the reported studies i.e.…”

“…Published by CBIORE high power requirement for gas compression and are mostly used at a commercial scale which facilitates bio-methane injection onto natural gas pipelines (Yousef et al, 2016). The necessity to increase raw biogas and water to high pressures while also in-putting energy for cooling the scrubbing water renders the HPWS process expensive due to the energy intensity required (Walozi et al, 2016). However, this high energy requirement could be offset by utilizing the NAPWS systems, which are reported to have lower specific power requirement, longer equipment lifespan, and requires no flashing process yet appropriate for smaller installations (Budzianowski et al, 2017).…”

“…Noorain et al, (2019) created a mathematical simulation model whilst using sponge carriers as packing materials and obtained a methane percentage of greater than 90%. Walozi et al, (2016) investigated the use of granite stones, candlenut seed, plastic balls, calcite marble and steel wire mesh in a low-pressure pilot scale scrubbing system and achieved a maximum purification methane concentration of 80%. These studies show that literature on the NAPWS utilizing conventional packing materials is limited.…”

Steam Explosion Pretreatment: Biomass Waste Utilization for Methane Production

“…The biogas purification for secondary energy was mandatory to get high content methane and to reduce the carbon dioxide (CO 2 ) to increase the density and the calorific value, and cleaning out the hydrogen sulfide (H 2 S) due to the corrosivity character for the metal part of in all the system such as gas storage tank, piping system, compressor, engine, and also the toxicity that harmful to the environment [89]. The CO 2 removal could be removed through physical absorption by water or organic scrubbing that could be physically bound with CO 2 [90,91]. The absorption using organic solvent could also remover the H 2 S, ammonia (NH 3 ), hydrogen cyanide (HCN) and also water vapor with low losses of CH 4 , and included into regeneration system with low temperature waste, however the operation and technology investment is expensive; chemical absorption by using di-methyl ethanol amine (DMEA) or mono ethanol amine (MEA), and solution of alkali such as NaOH, K2CO 3 , KOH, iron hydroxides (Fe(OH) 3 ), and FeCl 2 that could actively absorb the CO 2 [92,93]; pressure swing absorption by sequences process of adsorption, desorption, and pressurization by hiring the synthetic resin, zeolite, activated carbon, silica gel, or activated charcoal which also could separate the N 2 , H 2 S and O 2 [94]; cryogenic separation which takes advantage of the different boiling points of CO2 and CH4 by condensation process on gas cooling at elevated pressures that could separate the CO 2 and also the other gas content such as O 2 , N 2 and siloxanes [95]; membrane separation which base on the properties of the selective permeability of the membrane through two system i.e., gas-liquid separation where the liquid absorbs the CO 2 and also the H 2 S diffusing via the membrane, gas-gas separation by the gas phase from the both side of membranes [96,97]; hydrate formation which based on the equilibrium partition of the components between gaseous and hydrate phases, clathrate phase equilibrium for the water-phenol-carbon dioxide system [98,99].…”

The effects of adsorbent mass using red brick powder on the results of biogas purification

“…The Q value is positive, which means an increase in flow rate, increases the concentration of CH 4 after purification [25], [26]. This is because the addition of the flow rate to the red brick adsorbent containing a lot of silica-alumina will trap or bind CO 2 to the pores of the adsorbent due to van der Waals force and also the size of CO 2 which is larger than CH 4 , at that time also smaller CH 4 will pass through the adsorbent without being bound by the adsorbent, so the faster the biogas flow rate, the more CH 4 levels are obtained.…”