In the sewage treatment plant, anaerobic digestion process can be described as a major sewage treatment process, the main analysis of the design of anaerobic digestion process points, see below.

Anaerobic digestion process design is mainly reflected in the digestion tank type, mixing mode and process parameters on the choice. The overall design principles are: a) Optimum process parameters such as residence time, operating temperature, solid load, organic load are tested on the basis of similar project cases and design specifications; b) suitable pool type selection; c D) Simple and stable operation protection, such as equipment easy to operate and maintain, good heat exchange equipment to avoid temperature fluctuation and easy removal of scum; e) Safe and reliable Biogas delivery system.

Process design needs to be identified: a) the design of the digestion mode; b) the digestion tank shape selection; c) the mixing of the sludge in the digester; d) the selection of the design parameters; e) the determination of the sludge heating mode ; f) determination of sludge dosing method; g) determination of sludge and biogas emission modes; h) scum and supernatant removal methods; i) assurance of safety precautions; j) determination of monitoring and control methods ; k) the use of other ancillary equipment. Among the many aspects mentioned above, the way of anaerobic digestion, the shape of the digester, the main design parameters and the mixing method of the sludge in the digester have a great influence on the project cost and the use effect of the digester, and should be carefully chosen.

1 digestion design

① digestion temperature, anaerobic digestion according to different operating temperature is divided into temperature digestion (30 ~ 36 ℃) and high temperature digestion (50 ~ 55 ℃), of which the best temperature digestion temperature 35 ℃, high temperature digestion will be the best temperature will Due to other factors have undergone major changes. High-temperature digestion is characterized by fast decomposition rate, high gas production rate, short residence time, and then improve the digestive capacity, saving digester volume; other good health indicators, the parasite egg killing rate of up to 95% Escherichia coli index up to 10-100; high energy consumption, temperature control more difficult. The characteristics of mesophilic digestion are all the advantages of relatively high temperature digestion, but the mild digestion is stable and easy to control, the energy consumption is relatively low, and the design and operation experience is mature. At present, domestic and foreign more use of temperature anaerobic digestion.

â‘¡ digestion level, according to the number of digesters is divided into two levels of digestion and digestion. One of the digestion refers to sludge anaerobic digestion is completed in a digester; two digestion refers to sludge anaerobic digestion completed in two digesters, the first digester with heating, mixing device and gas collection device, not Row of supernatant and scum, the second stage of the digestion tank without heating and stirring, only the first level of waste heat to continue digestion, while row of supernatant and scum. The two-stage digestion process has a higher cost of civil engineering, more complicated operation than the first-level operation and a slight increase in the decomposition rate of organic matter, with the gas production rate being about 10% higher than that of the first-stage digestion. Based on saving investment costs and simple and stable operation, the current domestic use of more than one digestion.

2 digestive system type of choice

The standard digester should have good mixing, good scum removal foam conditions, good structural conditions and no dead zone and so on. There are many types of digestion ponds, there are three kinds of more commonly used, three kinds of digesters have their own advantages and disadvantages, applicable to different regions, through the following simple description for reference design.

Flat-bottomed cylindrical applications are more common in Europe, the height: diameter = 1. This flat on the circular mixing system requires a more single, more use of the pool can be installed more hanging spray-type biogas mixing technology.

Cylindrical cone at the end of more applications in China, the middle of the height: diameter = 1, up and down all cones, the bottom of the slope of 1.0-1.7, the top gradient of 0.6-1.0. Such digesters are conducive to the internal cycle, heat loss relative to the flat-bottomed cylindrical small, stirring system can be a good choice. The disadvantage is that the bottom of the larger volume, easy to accumulate sand, the need for regular clean-up. Also from the structural point of view, the conical part of the construction is difficult, and the stress concentration, the need for special treatment.

The oval digester is an improvement on the basis of a conical bottom cylinder, which has many advantages over the two types of digesters, such as: a) good agitation effect and difficult pooling of the bottom; b) certain pool capacity conditions The total surface area of ​​the cell body is small and the heat loss is small; c) the surface area at the top of the cell is small, the scum is easy to remove and the biogas is easy to collect; d) the structure of the oval structure is well-stressed to save building materials;

3 digestion tank mixing method of choice

Anaerobic digestion is the contact reaction between the cell and the substrate. During the reaction, it is necessary to mix the two sufficiently, so stirring becomes very important. Through the design of a reasonable way of mixing, the following objectives are achieved: a) the fresh sludge is thoroughly mixed with the digestive sludge rich in digestive bacteria to speed up the reaction; b) the gas is separated from the sludge smoothly and overflows the liquid surface; c) System temperature and PH remain uniform, to avoid the influence of digestive bacteria by temperature and PH changes; d) to prevent a large number of scum generated in the pool.

There are three types of commonly used mixing methods, namely: gas mixing, mechanical mixing (including mechanical impeller mixing, mechanical lifting circulating mixing) and sludge circulation mixing. Domestic and foreign often use the mixing method is biogas mixing and mechanical mixing, sludge pump cycle because of large power consumption, poor mixing effect is rarely used. In the blender design choices, we must consider the digestion tank shape, volume, investment costs and operation and management requirements. Here are some commonly used mixing equipment:

Pultruded Tube And Rod

Carbon Fiber Bar,Carbon Fiber Pultruded Rod,Pultruded Carbon Fiber Rod,Pultruded Carbon Rod

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