Removal of H2S from biogas by activated carbon: Nablus Western Wastewater Treatment Plant as a Case Study
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Date
2022-06-06
Authors
Dunia Ahmad Jazi
Reem Khalil Takrouri
Shaimaa Ra'fat Bani Mineh
Shaimaa Munther Hamadneh
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Abstract
Biogas, produced from anaerobic digestion of animal manure and waste water is an attractive alternative energy source as it is rich in methane. However, it is necessary to remove hydrogen sulfide from the biogas before it can be used in engines for electricity generation. Currently, large scale biogas systems employ physical absorption solvents to upgrade and purify biogas which is not economically feasible for small scale biogas systems. Activated carbon proves to be an effective adsorbent of hydrogen sulfide. Mathematical models for adsorption column such as Adam-Bohart and Thomas models were used. To predict the adsorption capacity, and breakthrough curves for this carbon material. The parameters like inlet H2S concentration, flow rate, and mass of activated carbon were analyzed using Thomas model. However, the effect of bed height was investigated using Adam-Bohart model. The results showed that when the initial concentration was reduced, the adsorption efficiency increased; at the change of initial concentration from 1400 ppm to 400 ppm the breakthrough times were 21 and 76 days for initial concentration of 1400 and 400, respectively. It was also found that decreasing the flowrate of the treated gas, resulting in a shorter breakthrough time. The breakthrough time increased as the flow rate and initial H2S concentration were reduced; the breakthrough time was 86 days when the flow rate was 0.0125 L/s and it was 36 days when the flowrate was 0.03 L/s. The results also show that the H2S removal efficiency increased as the bed height increased.
In this study, based on the results, the best configuration of the bed height, flowrate, and adsorbent mass were 10 m, 0.0125 L/s, and 200 kg respectively. Two parallel columns will be utilized with adsorbent mass of 200 kg for each column, and the initial concentration of H2S of 1400 ppm for each column. As a result of the high efficiency of adsorption at a low concentration, it is preferred to reduce this concentration to 400 ppm using other methods, such as biological treatment.
The regeneration of spent activated carbon was systematically studied by thermal regeneration method, and the number of times required for this method was calculated, which was once every three months. The annual used amount of activated carbon was 512 kg and its cost is $194/year according to the required times for regeneration..