Application Of Biological Desulfurization Technology Of Biogas

In the safe application of clean energy such as biogas,it is necessary to remove hydrogen sulfide.Compared with chemical desulfurization,biological desulfurization is widely used due to its advantages,such as mild operation conditions,high removal efficiency of hydrogen sulfide,no catalyst,less energy consumption and little waste liquid.Alkali biological desulfurization technology has many advantages,such as elemental sulfur as the main oxidation product,high absorption efficiency of hydrogen sulfide,short residence time in absorption tower and small volume of desulfurization tower.In order to accelerate the development of biological desulfurization technology,the biological desulfurization project of Paques was investigated.The handling capacity of desulfurization project was 10000m³/d and the H₂S concentration in biogas was 3000 ppm,the removal efficiency of H₂S is 96.7%.Maximum salinity of circulating liquid was2.72%during operation.The nutrients used in alkali biological desulfurization of Paques are basically the same as those used in previous experiments.The mass ratio of KH₂PO₄,MgSO₄ and CO（NH₂）₂ in solution is 0.48:0.30:0.22.Aiming at the problem that it is difficult to control the oxidation products of sulfide in alkaline biological desulfurization,the effects of operating parameters,such as sulfide concentration,salinity,dissolved oxygen concentration（DO）,temperature,oxidation-reduction potential（ORP）,on alkaline biological desulfurization were studied in a batch reactor.The results indicate that when the initial sulfide concentration is500 mg/L,the desulfurization process can be divided into three stages:fast removal,pause and slow degradation.In the fast removal stage,the sulfide concentration decreased rapidly to 320 mg/L for 50 min.Meanwhile,the pH increased from 7.0 to 8.6.In the pause stage,the concentration of sulfide remained around 320-280 mg/L for 80 min.The pH decreased slowly.In the slow degradation stage,sulfide concentration dropped to below 10 mg/L at uniform speed.The desulfurization rate was low,and the pH was gradually reduced.In the fast removal stage,there is high desulfurization efficiency and the maximum elemental sulfur productivity.At this same time,the ORP was kept stable at about-400mV.At the conditions of the salinity of 3.5%,the temperature of 30℃and dissolved oxygen concentration of 2 mg/L,the desulfurization reaction can be maintained in the fast removal stage,and high efficiency desulfurization can be achieved by controlling the ORP at around-400mV.The biogas desulfurization tower was designed for the handling capacity of 36000 m³/d with 5000ppm hydrogen sulfide in the biogas.The remova efficiency of H₂S is over 97%.The design results show that packing of absorption tower is 50 mm plastic Pall ring;the ratio of gas and liquid is 11.63:1;the diameter of absorption tower is 1800 mm;the packing height is 8.8 m and the total pressure drop is 774.2 pa.The process of hydrogen sulfide absorption in biological desulfurization project was simulated and analyzed by Aspen Plus process simulation software.The results showed that the optimum gas-liquid ratio was11.55:1,flow rate of absorbent was 130.25 m³/h.The results show that molar fraction of H₂S gas in the treated biogas is less than 1.5×10^-4,when the diameter of the tower is 1.7 m and the packing is 50 mm plastic pall ring,and the simulation results are in good agreement with the calculation,it is reasonable to design and calculate absorber parameters.According to the optimized parameters,a biogas desulfurization biological system is designed.The desulfurization system consists of hydrogen sulfide absorption tower,bio-regeneration reactor,aeration device,dosing device,circulating water device,heating and refrigeration device,related auxiliary equipment and instruments.The height and the diameter of absorber tower is 16 m and 1.8 m,respectively.The height and the diameter of bioreactor is 3.5 m and 2.4 m,respectively.Its strength design and stability results meet the requirements.The cost of biogas treatment per cubic meter is 0.023 yuan.The biogas desulfurization project was debugged on site.After 17days of debugging,the desulfurization efficiency gradually increased to95.30%.During debugging,the pH is controlled between 7.5 and 8.5,temperature is controlled at 30℃,and salinity is controlled at 0-3.5%.In the stage of stable and efficient operation of biological desulfurization system,ORP value is maintained within-380 mV to-400 mV,DO concentration is between 1-2 mg/L,total alkali dosage is 75 kg/d,and alkalinity of circulating liquid is maintained at about 0.30 mol/L.The concentration of H₂S finally decreased to 131 ppm,and the biological desulfurization system worked well.