Breakthrough in biomass energy utilization

handong Minhe Animal Husbandry Ltd. Co. has a special chicken farm in Penglai, Shandong. Being the biggest exemplary broiler farm in China, the Minhe chicken farm surprises us with its ground totally free from chicken manure and wastewater. We cannot but wonder: Where has all the chicken manure gone? It turns out that the chicken manure is transported through belt and underground piping work to a homogenized hydrolysis tank, in which the manure is stirred, mixed, hydrolyzed and then conveyed to ferment into biogas in an anaerobic biogas tank.

Biogas is an eco-friendly energy source that is becoming increasingly important in today's energy supply. It can be used to generate power or heat or as fuel, and provides high energy yield per square meter of land. However, only about 40% of its energy is consumed if the biogas untreated is directly converted into electricity power. But if the biogas goes through efficient upgrading and purification, a process in which CO2 is separated and the biogas becomes biomethane meets the state standard of natural gas, 90% of the energy can utilized.

The common separation methods, such as pressurized water scrubbing, pressure swing adsorption, and amine scrubbing, have considerable disadvantages: They need comparatively large amounts of energy as well as auxiliary materials and chemicals. Wastes and wastewater that are subsequently generated must be treated and disposed properly. The latest membrane separation technology, however, would waste a large quantity of biogas due to the low selectivity of the membranes. In addition, the complicated process of connecting membranes together in series increases investment and maintenance costs. 

Evonik Industries from Germany has developed a technology for cost- and energy-efficient separation of CO2. What appears at first sight to be a bunch of spaghetti strands or a paint brush is in fact a bundle of highly selective membranes made up of multiple high-performance cylindrical polymer fiber with very high temperature and pressure resistance. These new hollow fiber membrane modules of SEPURAN® Green boost the separation capacity effectively between methane and CO2. 

The gas separation membrane SEPURAN® Green works on the principle of selective permeation through a membrane surface. The driving force for permeation of the gas through the membrane is the difference between the partial pressures of the gas on the interior of the hollow fiber and the exterior side. In the upgrading process, CO2 in the biogas permeates through the membrane, while the methane stays inside the membrane. 

In September 2013, equipment that has adopted Evonik SEPURAN® Green membrane technology was introduced into the chicken farm of Shandong Minhe and was tested in its first biogas plant. After pretreatment, the biogas generated from chicken manure was purified through the three-stage SEPURAN® Green upgrading membrane systems. Separated from CO2, methane that meets the first class standard of natural gas was then produced from biogas. With a methane yield up to 99.5%, the off-gas was fairly clean and contained significantly less than 1% methane. 

Satisfied by the good result, Shandong Minhe decided to use Evonik SEPURAN® Green technology in their second biogas plant. Working jointly with its long-term partner EnviTec Biogas, a famous biogas equipment manufacturer from Germany, Evonik will help to establish the first three-stage biogas purification system in China. When the construction is completed, 70,000m3 biogas generated from 700t chicken manure will be converted each day into 40,000m3 of biomethane. The product will be fed into the natural gas grid directly to supply the surrounding villages, or compressed to serve as automotive fuel. This project is expected to be put into operation by the end of the year.