Analysis of Key Points of Anaerobic Digestion Process Design (Part 2)

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Selection of mixing method in the digester

Anaerobic digestion system contact with the substrate of the reaction is bacteria, both need to make the fully mixed in the reaction process, so the mixture becomes very important. By designing a reasonable mixing method, the following objectives can be achieved: a) the fresh sludge can be fully mixed with the digested sludge rich in digestive bacteria to speed up the reaction speed;B) make the gas separate from the sludge smoothly and overflow the liquid level;C) keep the temperature and PH of the system uniform, and avoid the influence of temperature and PH changes on the digestive bacteria;D) prevent the formation of large amounts of scum in the pool.

There are three kinds of common stirring methods, which are gas stirring, mechanical stirring (including mechanical impeller stirring, mechanical lifting circular stirring), and sludge circular stirring. The domestic and foreign stirring methods are biogas stirring and mechanical stirring, and the sludge pump circulation method is rarely used due to the large power consumption. In the design and selection of agitators, the shape, volume, investment cost, and operation management requirements of digester should be considered comprehensively. The following are some common stirring devices:

1

Propeller mechanical agitator

Propeller-type mixing equipment is simple in composition, easy in operation, and small in maintenance. It can push the sludge upward or downward through the standpipe. Therefore, on the premise of fixing the sludge liquid surface, it can effectively eliminate the scum layer. However, when the propeller in the pool breaks down, the digestive system should stop running and enter the internal maintenance. The processing capacity of the propeller agitator was characterized by the number of times in one day the sludge from the digester was completely stirred or the time it took to complete a single stirring.

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(2) suspension nozzle biogas agitator

The suspended nozzle biogas agitator consists of a biogas delivery standpipe and a nozzle suspended at the top of the tank. The agitators can be arranged at multiple points in the pool as needed and can be run in groups. Simple structure; Flexible setup and operation; Because it can be stirred in groups, the required stirring intensity is small; Strong adaptability to the pool; Not subject to liquid level control and other advantages. This type of agitator is suitable for the various pool shapes mentioned above and shows its advantages in the flat bottomed or tapered lower digester. The performance of the agitator is the same as that of the propeller agitator.

Anaerobic digestion system 

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Multi-beam tube biogas agitator

The multi-beam tube biogas agitator is composed of a multi-beam biogas conveying pipe (the beam pipe) and a biogas release port. The beam tube enters the pool from the middle of the top of the digester and extends to the outlet at the bottom of the pool. This agitator is characterized by its simple structure and easy operation. However, it is easy to block, so it is necessary to add an observation ball and high-pressure water washing device at the end of each beam tube on the top of the pool. Due to the setting of the methane outlet, it is concentrated in the middle of the bottom of the pool, which is suitable for the pool with a small diameter and a large slope. The selection of agitator depends on the volume of the whole tank.

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At the bottom of a number of blowpipe biogas agitator

The bottom of the multi-blowpipe biogas agitator is mainly composed of a multi-pipe biogas conveyer and a biogas release port. The biogas pipe can enter from the sidewall at the top of the tank or the side of the tank, and extend along the bottom of the tank to the middle of the tank and connect with the biogas outlet. Similar to the multi-beam tube biogas agitator, this type of agitator is characterized by its simple structure and easy operation. However, it is easy to block, because the biogas release port is located in the middle of the bottom of the pool, which is suitable for the pool with a small diameter and a large slope. The selection of agitator is based on the volume of the whole tank.

Among the four common agitators mentioned above, the propeller mechanical agitator is a mechanical agitator, and the other three are all biogas agitators. This is mainly because biogas mixing has many advantages: a) the flow of biogas drives the internal circulation of sludge;B) the turbulence effect prevents the generation of scum, the mixing effect is good and the gas separation effect is improved;C) the use of biogas does not need to consider the tank type and liquid level. There are also some disadvantages of biogas mixing: a) the composition is complex, generally including biogas compressor, biogas injection pipe, biogas recycling pipe, condensate water discharge equipment, and biogas filter, etc., resulting in complex operation management; B) firedamp is a flammable and explosive gas, and equipment for firedamp requires special safety measures.

Compared with anaerobic digestion, aerobic digestion aims at producing stable products through the oxidation of biodegradable organic matter, reducing mass and volume, reducing pathogenic bacteria, and improving the characteristics of sludge for further treatment.

Aerobic digestion is usually used in sewage plants with a treatment capacity of less than 1.89×104m3/d, and the primary sludge is usually mixed with the secondary sludge for digestion, at which time the oxygen demand is greater than that for the treatment of individual biological sludge. The digestion tank should be equipped with grills and slag skimming equipment. The inlet water should not contain high inorganic substances and should be ground to prevent the blockage of the aeration equipment. Even so, the aeration facilities still need to be fully considered to prevent the accumulation of grease and scum on the surface of the digester.

Analysis of Key Points of Anaerobic Digestion Process Design (Part 1)

 Anaerobic digestion system process design mainly embodied in the digester type, mixing method and process on the choice of operating parameters.The general design principles are as follows: a) on the basis of reference to similar engineering cases and design specifications, the optimal process operation parameters, such as residence time, operating temperature, solid load and organic load, are obtained through experiments;B) suitable pool type selection;C) good mixing method, mixing evenly, no dead corners;D) simple and stable operation guarantee, such as equipment that is easy to operate and maintain, good heat transfer equipment that avoids temperature fluctuations, and measures to remove scum easily;E) safe and reliable biogas delivery system.

Content to be determined in process design: a) design of digestion mode;B) selection of digester shape;C) determine the mixing method of sludge in the digester;D) selection of design parameters;E) determination of sludge heating method;F) determination of sludge allocation method;G) determination of sludge and methane emission modes;H) removal method of scum and supernatant;I) guarantee of safety and protection measures;J) determination of monitoring and control methods;K) selection of other ancillary devices.Among the above aspects, the way of anaerobic digestion, the shape of the digester, the main design parameters and the mixing and mixing method of the sludge in the digester have great influence on the construction cost and use effect of the digester, which should be selected carefully.

1

The design of the digestion method

(1) digestion temperature, anaerobic digestion according to the operating temperature of different divided into medium temperature digestion (30 ~ 36℃) and high temperature digestion (50 ~ 55℃), in which the best temperature of medium temperature digestion is 35℃, the best temperature of high temperature digestion will be due to other factors will have a greater change.High temperature digestion is characterized by fast decomposition rate, high gas production rate and short residence time, thus improving the digestion capacity and saving the digester volume.In addition, the hygiene index was better, the killing rate of parasitic worm eggs could reach 95%, and the coliform index could reach 10-100.High energy consumption and difficult temperature control.The characteristics of medium-temperature digestion are that compared with the advantages of high-temperature digestion, the medium-temperature digestion is stable, easy to control, relatively low energy consumption, and has mature design and operation experience.At present, the domestic and external use of medium temperature anaerobic digestion.

(2) digestion level, according to the number of digestion tank divided into one digestion and two digestion.Primary digestion refers to sludge anaerobic digestion is completed in a digester;Two-stage digestion refers to the anaerobic digestion of sludge is completed in two digesters. The first-stage digester is equipped with heating, stirring device and gas collection device, and no supercleaning liquid and scum are discharged. The second-stage digester is not heated and stirred, and only the remaining heat of the first stage is used to continue digestion, and the supercleaning liquid and scum are discharged at the same time.The cost of the two-stage digestion process is relatively high, and the operation is more complicated than that of the first-stage digestion. The decomposition rate of organic matter is slightly improved, and the gas production rate is about 10% higher than that of the first-stage digestion.Based on the savings of investment costs and simple and stable operation, the current domestic use of a digestion.

Anaerobic Digestion Plant

2

Selection of anaerobic digestion plant

A standard digester should be characterized by good mixing and agitation, good scum foam removal conditions, good structural conditions, and no dead zone. There are many types of the digester, and there are three kinds of digester in common use. The three kinds of digester have their own advantages and disadvantages, which are suitable for different regions. The following simple description can provide a reference for the design.

The flat cylinder is more common in Europe, height: diameter = 1. This kind of flat - bottomed circular mixing system has a single requirement, and most of them adopt the hanging injection biogas mixing technology which can be installed at multiple points in the tank.

Cone bottom cylinder is widely used in China, where the height: diameter =1, the top and bottom are cones, the bottom slope is 1.0-1.7, and the top slope is 0.6-1.0. This type of digester is conducive to internal circulation, with less heat loss than the flat bottom cylinder, and a good mixing system. The disadvantage is that the bottom volume is large, easy to accumulate sand, need to be cleaned regularly. In addition, from the structural point of view, the cone part is difficult to construct, and the stress set, need special treatment.

The oval digester is an improvement on the cylindrical shape of the cone bottom. The shape of the digester has many advantages for the above two types of digesters.B) under certain pool capacity conditions, the total surface area of the pool body is small and the heat loss is small;C) small surface area on the top of the tank, easy to remove scum and easy to collect biogas;D) structurally, the egg-shaped structure bears good stress and saves building materials;E) beautiful appearance.

The Damage of the Hydraulic Metal Baler Lying Idle for Too Long

 The hydraulic baling machine gradually loses its original performance during use or idle, or the performance is poor compared with similar new equipment, and the phenomenon of the old style is called equipment degradation.

1. The degradation of hydraulic metal baler can be divided into use degradation, natural degradation and disaster degradation. Use degradation refers to the damage and deformation caused by wear and corrosion caused by wear and corrosion, impact, fatigue, and panning during the use of the equipment, the adhesion of raw materials and the pollution of dust and other phenomena, causing the equipment to lose its original Performance. Natural deterioration refers to the phenomenon of aging of materials with the passage of time or by the influence of the atmosphere after the equipment enters the factory, or suffering from external disasters and accelerating the speed of this aging. Disaster deterioration refers to the phenomenon that equipment is damaged or equipment performance is reduced due to natural disasters such as storms, flooding, earthquakes, lightning strikes, and explosions.

2. The equipment deterioration of hydraulic cardboard baling machine china can also be divided into absolute deterioration and relative deterioration. Absolute degradation is the aging of equipment, that is, as time passes, the equipment gradually wears out and gradually aging until it needs to be scrapped. Relative deterioration refers to the phenomenon that the original equipment and the new equipment have low performance and poor quality, so they appear old-fashioned.

The deterioration of the equipment leads to a reduction in the technical performance of the equipment, or the technical performance of the original equipment is poor compared to the new equipment. If you look at the economic value of the equipment, its value also decreases over time, which is also called economic degradation.

The deterioration of the equipment reduces the performance of the equipment, increases the number of failures, increases the maintenance costs, reduces the output of the products it produces, reduces the quality, increases the cost and cannot guarantee the delivery on time, and the staff's sense of security and mood decrease, causing various losses.

Hydraulic Cardboard Baling Machine China

3. There are two compensation methods for equipment degradation: one is to replace the old equipment that has been deteriorated or worn out with new equipment, that is, to update the equipment; the second is to perform local compensation through maintenance during the use process. Because the service life of equipment parts is uneven, it is of great economic significance to use a repair method to compensate locally.

4. The cycle diagram of equipment degradation can be seen that the equipment enters the production period from the construction period. Its performance gradually reaches the design level and enters the stable production period. After further innovation, the performance of the equipment will be further improved and the normal production period will be entered. The equipment gradually deteriorates in use, and every time it is repaired, a certain performance is restored, but the performance of the equipment still shows a downward trend. At this time, if the transformation is carried out, the performance of the equipment may approach the new generation of equipment. When the performance of the equipment deteriorates sharply and it is not worth the repairs, it should be updated.

The Significance of Compressed Packer in Waste Sorting

 Waste classification and treatment is the development direction of waste treatment. In view of the various shortcomings of the current garbage disposal methods, the sorting and sorting work before garbage collection or landfill will make the number of useful substances in domestic garbage, the amount of compost and even the amount of incineration significantly increase, and the amount of direct landfill It will be greatly reduced, not only saving a lot of lands, reducing secondary pollution, but also significantly improving the utilization rate of garbage resources. In order to fully realize the reduction, recycling, and harmlessness of waste disposal, and achieve a circular economy, a solid foundation is laid.

The classification and treatment of domestic waste is a waste treatment method suitable for use in urban streets, communities, and townships. In the waste sorting and processing station, through closed transportation, screening, magnetic separation, bounce, wind separation, packaging, pressing, deodorization, deodorization Disposal procedures such as smell, and thorough sorting of municipal solid waste according to nature and final treatment method. The first category is recyclable substances, such as plastics, rubber, paper shells, metals, etc .; the second category is available for Composting materials, such as vegetables, melon fruit shells, leaves, etc .; the third category is materials that can be directly landfilled, such as bricks and tiles, stones, sand, etc., and then these sorted garbages are subjected to compression and volume reduction treatment Transported to a special factory for recycling or composting or direct landfill. Therefore, as a prerequisite for post-processing methods such as filling, composting, recycling, and incineration, garbage classification treatment can achieve the ultimate goal of reducing, recycling, and harmless urban household waste.

With the development of the urban economy and the improvement of residents' living consumption level, while the output of urban waste continues to increase, the composition of urban domestic waste is also very different. The main characteristics of the change are: high content of the waste paper, plastic, plant fiber It is particularly prominent, which has caused the proportion of organic ingredients in the waste to continue to increase, and the phenomenon of rapid volume growth and slow weight growth has occurred. According to the research and analysis of the density of urban garbage, the density of garbage has dropped from the previous 600kg / m 'to the current 350kg / m, and there is a trend of gradual decrease. Therefore, a large number of light materials such as plastics, paper shells, and plant fibers will be screened out after the municipal solid waste is sorted and processed. This part of the waste is suitable for recycling and recycling. Due to the lightweight and large volume of these wastes, the transfer efficiency is low. Transportation and storage costs are high, a lot of manpower and material resources are wasted, and the cost of garbage disposal is increased.

Plastic Baler Machine

With the development of urban garbage compression and volume reduction and consolidation, the requirements for plastic baler machines have gradually increased. Compression packing devices with high compression ratio, intelligence, high reliability, high efficiency, durability, and simple and reasonable structure will become the general trend of research. The improvement of garbage compression and packaging efficiency can effectively reduce the cost of garbage disposal, so the research on compression and packaging equipment has good social and economic benefits. Domestic and foreign urban domestic garbage compression and packaging equipment are developing in the direction of small space, high efficiency, and high compression ratio. The key to reducing the volume of garbage is to use an efficient and practical recycling baler machine.

The development of household garbage compression packers and their placement in urban streets, communities, and townships can reduce waste transportation input and avoid transportation of garbage. To improve the efficiency of transshipment and save costs, the design and development of urban domestic garbage compression and packaging equipment are of great significance.

 

 

Current Situation of Municipal Solid Waste Disposal (Part 2)

 (2) composting: scientific research on composting techniques began in the 1920s in the Netherlands. Composting treatment refers to the conversion of the organic matter in the garbage into stable humus under artificial control, so as to make it a soil improver that can be applied to the farmland. Composting technology is relatively simple, suitable for waste disposal with high perishable organic matter content, can make use of some components in waste resources, and the investment of waste disposal in the same quality is greatly reduced compared with the simple incineration treatment. Composting must be a process in which fresh waste is first sorted before the perishable organic components are fermented. At present, the number of waste compost plants abroad is on the decline, but the development of composting technology has not stopped, the most widely used is mechanical biotechnology (MBT).

(3) incineration method: incineration method is a high-temperature heat treatment technology, that is, with a certain amount of air and garbage in the incinerator for oxidation combustion reaction, the harmful toxic substances in the garbage in the high-temperature oxidation, pyrolysis and destruction. The incineration method has obvious capacity reduction effect, a high degree of innocency, short treatment period, small area, and has been widely used in developed countries. Incineration treatment technology is characterized by large capacity, good capacity reduction, complete innocency, the heat generated by the incineration process can be used to generate electricity to achieve the energy of waste. At present, there are more than 200 kinds of waste incinerators in use all over the world, but there are four representative types, which are widely used: fluidized bed incinerator technology, rotary kiln incinerator technology, grate incinerator technology, and waste pyrolysis gasification incinerator technology. At present, the most widely used domestic waste treatment is mechanical grate furnace, followed by fluidized bed furnace, rotary kiln incineration and pyrolysis gasification incineration account for a small proportion, mainly used for the treatment of hospital garbage and chemical waste. Domestic garbage treatment methods mainly include sanitary landfill, incineration, composting, etc. In order to achieve the best treatment effect, different regions will reasonably choose one or several methods according to local conditions to conduct garbage treatment.

At present, the proportion of landfills, compost, and incineration is about 92.2%, 2.6%, and 5.2% respectively. The proportion of recyclable resources and organic perishable compost is too small and the proportion of landfills is too large. The reason for this phenomenon is that the garbage is not completely or completely separated from the direct landfill, not only waste resources, occupy a lot of lands, but also increase the transportation cost, causing secondary environmental pollution.

Recycling Sorting Equipment

China garbage sorting machine msw manufacturer believes that garbage Sorting is the development direction of garbage disposal. In garbage classification collection or work on the classification of the sorting before landfill, recycling sorting equipment makes the use of living garbage in the useful material dosage, compost and even burning amount will be significantly improved, direct landfill quantity will be reduced greatly, not only save a large amount of land but also reduce the secondary pollution, can significantly improve the resource utilization of waste.