以富CO2吸收液为汲取液的沼液中水正渗透回收特性研究

Performance of Water Recovery from Biogas Slurry by Forward Osmosis Technology when Adopting CO2-rich Solvent as Draw Solution

摘要:

针对沼气工程存在的沼液量大难处理问题及沼气提纯的需求，提出将正渗透技术与沼气CO2化学吸收分离耦合，探究了沼气CO2化学吸收中的富CO2吸收液作为正渗透汲取液从沼液中回收水及浓缩沼液的可行性，并以沼液浓缩过程中的水通量、沼液浓缩倍数、沼液氨氮截留率与吸收剂反向传质通量为指标，考察了汲取液种类、汲取液浓度与其他操作参数对正渗透水回收性能的影响。结果表明，富CO2吸收液作为汲取液从沼液中回收水并浓缩沼液具有可行性，且随着汲取液浓度、流量和温度的增加，沼液中水向汲取液的传质通量增加，沼液浓缩倍数也相应增加，但沼液中氨氮截留率下降，同时汲取液中的吸收剂溶质向沼液的反向传质通量也增加。当采用浓度2.5mol/L、CO2负荷0.5mol/mol的富CO2甘氨酸钾溶液作为汲取液，汲取液温度为70℃、流速为150mL/min、沼液室温及流速为150mL/min时，采用正渗透技术从沼液中回收水的初始通量达8.05L/（m2·h），经过4h运行后，沼液浓缩倍数为1.18，氨氮截留率为84.13%，反向吸收剂通量仅为2.94g/（m2·h）。

Abstract:

In the biogas project, determining how to treat the biogas slurry with large volume is one of big issues. Additionally, biogas upgrading is always required for increasing the heat value of biogas. A concept was proposed by coupling the water recovery using forward osmosis and CO2 chemical absorption, in which the CO2-rich solvent from CO2 chemical absorption process was adopted as the draw solution to recover water from biogas slurry in forward osmosis. The feasibility of water recovery from biogas slurry by using CO2-rich solvent as the draw solution in addition to concentrating the biogas slurry was experimentally investigated. In terms of the water flux, concentration ratio of biogas slurry, rejection ratio of ammonia nitrogen and CO2 absorbent transfer flux from the draw solution to biogas slurry, effects of the type and mass fraction of draw solution and other key operation parameters on water recovery performance in forward osmosis were explored. Results showed that CO2-rich solvent can be adopted as the draw solution to successfully reclaim water from biogas slurry and simultaneously concentrate the biogas slurry in forward osmosis. Additionally, the water flux transferred from biogas slurry from the draw solution increases with the mass fraction, flow rate and temperature of draw solution. Correspondingly, the concentration ratio of biogas slurry was increased, however, the rejection ratio of ammonia nitrogen in biogas slurry was decreased and the absorbent transfer flux of CO2 absorbent was increased. When the CO2-rich potassium glycinate with 2.5mol/L and 0.5mol/mol CO2 loading was adopted as the draw solution in the forward osmosis, the initial water flux from biogas slurry was about 8.05L/(m2·h) at the conditions of 70℃ and 150mL/min for draw solution, and ambient temperature and 150mL/min for biogas slurry. After 4h operation, the concentration ratio and ammonia nitrogen rejection ratio of biogas slurry can reach 1.18 and 84.13%, respectively. Notably, the CO2 absorbent transfer flux was only 2.94g/(m2·h). The research result may provide a technical support for concentrating biogas slurry and recovering water from biogas slurry.