Bio Engine Composting Part 2
Classification by type of fermentation plant
According to the type of fermentation device, there are vertical composting fermentation tower, horizontal composting fermentation drum, silo composting fermentation tank and box composting fermentation tank.
1 vertical compost fermentation tower
Vertical composting fermentation tower usually consists of 5-8 layers. The composting material enters the tower from the top of the tower. In the tower, composting moves from the top of the tower to the bottom of the tower through different forms of mechanical movement. Generally, after 5 to 8 days of aerobic fermentation, the compost is moved from the top of the tower to the bottom of the tower to complete a fermentation. Vertical composting fermentation tower usually has a closed structure. The temperature distribution in the tower gradually increases from the upper layer to the lower layer, that is, the lowest layer has the highest temperature. In order to ensure the activity of microorganisms in each layer for high-speed composting and maintain the optimum temperature and ventilation volume of microorganisms in each layer of the tower respectively, the oxygen supply of the tower device is usually forced ventilated by a fan, and the air is quantitatively ventilated into the tower through the vents of different heights installed on the side of the tower body to meet the micro-generation. The demand for oxygen.
Vertical composting fermentation tower usually includes vertical multi-stage cylinder type, vertical multi-stage landing gate type, vertical multi-stage blade scraper type, vertical multi-stage movable bed type, etc.
2 horizontal composting fermentation drums
Horizontal composting fermentation drum is also called Danot type. The main equipment is a horizontal drum with a length of 20-35 m and a diameter of 2-3.5 M. In the fermentation device, waste is raised along the rotating direction by friction with the inner surface of the cylinder, and falls down by means of self-weight. By rising and falling repeatedly, the waste is evenly turned over and contacted with the air supplied, and fermented by microorganisms. In addition, because the cylinder is oblique, when the waste lifted along the rotating direction falls by its own weight, it gradually moves to one end of the outlet of the cylinder, so that the rotary kiln can automatically and steadily supply, transport and discharge compost. The processing conditions of the device are summarized as follows:
The ventilated air temperature is normal in principle. For a 24-hour continuous operation device, the ventilation rate is 0.1 m3/(m3.mm), and the rotating speed of stirring in the cylinder should be 0.2-3.0 r/min. If the whole fermentation process is completed in this device, the residence time should be 2-5 days. The filling rate of cylinder is generally as follows: waste volume in cylinder/cylinder capacity is less than capacity. The average temperature of compost in the whole fermentation process is 50-60 when the device is used, and the maximum temperature can reach 70-80 high. When the device is used for one fermentation, the average temperature is 35-45, and the maximum temperature can be about 60 high.
3 silo type compost fermentation silo
Silo-type compost fermentation silo is a single-layer cylindrical (or rectangular) fermentation silo, the depth of fermentation silo is generally 4-5 M. The upper part is provided with a feed inlet and a scraper diversion device, and the lower part is provided with a screw discharger. Most of them are made of reinforced concrete. High-pressure centrifugal fan was used to supply oxygen in fermentation chamber to maintain aerobic fermentation of compost in fermentation chamber. Air generally enters the fermentation bin from the bottom of the silo, and composting material enters from the top of the silo. After 6-12 days of aerobic fermentation, the compost with initial maturity was discharged from the bottom of the silo through the discharger. According to the movement form of compost in fermentation bin, silo fermentation bin can be divided into static and dynamic.
(1) Silo-type static fermentation bin.
The device is a single-layer cylinder with stacking height of 4-5 M. The compost enters the silo through the distributor from the top of the silo. After 10-12 days of aerobic fermentation, the compost is discharged by the screw discharger at the bottom of the silo. Because there is no repetitive cutting device in the warehouse, the raw materials are compacted and lumpy, the ventilation performance is poor, the ventilation resistance is large, the power consumption is large, and the product is difficult to homogenize. However, the device occupies a small area and has a high utilization rate of fermentation bin, which is its advantage. The structure of this device is simple, so it is widely used.
(2) Silo-type dynamic fermentation silo.
The silo-type dynamic fermentation silo is a single-layer cylindrical silo with a stacking height of 1.5-2 M. During the operation of the dynamic fermentation bin, the crushed wastes sorted by the pretreatment process are transferred to the middle of the top of the tank by the feeder, and then uniformly distributed by the feeder to the tank. The screw drill located in the rotating layer stirs the wastes in the tank by revolution and rotation, so as to prevent the formation of grooves, and the shape and arrangement of the screw drills can pass through. Maintain a uniform distribution of air. Waste falls from the top down in the pond by gravity. Rotary cutting screw device with revolution and rotation is installed at the bottom of the pool. Whether the upper rotating layer rotates or not, the product can be discharged from the bottom of the pool. The air required for aerobic fermentation is forced into the bottom of the pond through the air distribution board. In order to maintain the aerobic environment in the pond and promote fermentation, forced ventilation from the bottom of the pond was adopted by blower. By measuring the temperature and gas concentration in each section of the pool, the air quantity supplied to each section can be adjusted and the rotation period of the bridge tower can be controlled to change the overturning frequency. The period of one fermentation is 5-7 days. In the composting process, the helical blades cut off the raw materials repeatedly, and the raw materials are pressed on the helical surface, which is easy to produce compacted lumps, so the ventilation performance is not very good. In addition, it also has some shortcomings, such as uneven residence time of raw materials, uneven product shape and not easy to seal. Its advantage is that the height of the outlet and the residence time of the raw material can be adjusted.
4 Box composting fermentation tank
There are many kinds of box-type composting fermentation ponds and their applications are very common. The main classifications of box-type composting fermentation ponds are as follows:
(1) Rectangular fixed plough-shaped overturned fermentation tank.
The box-type composting fermentation pool is equipped with plough-type upside-down mixing device. The device acts as a mechanical plough to dig waste. It can regularly agitate and move materials several times. It can keep the ventilation in the pool, make the materials evenly disperse, and also has transportation function. It can move materials from the feed end to the discharge end, and the materials stay in the pool for 5-10 days. The air is forced to ventilate through the air distributor at the bottom of the pool. Fermentation tank adopts conveying mixing device, which can increase the height of material accumulation.
(2) Fan bucket overturned fermentation tank.
This kind of fermentation tank is horizontally fixed. It is equipped with a dumper to mix the waste so that the humidity of the waste is uniform and in contact with the air, which promotes the rapid decomposition of compost and prevents the generation of odor. The residence time is 7 to 10 days. The frequency of dumping waste is once a day as the standard. The number of dumping can also be changed depending on the material properties. The fermentation plant has several characteristics in operation: the fermentation tank is equipped with a mixer and an overturning car mounted on the truck conveyor. When the waste is overturned, the overturning car runs on the fermentation tank. When the overturning operation is completed, the overturning car returns to the movable car. According to the handling capacity, sometimes the traveling crane structure can not be installed. Vehicle conveyor; When the material in the pond is overturned, the mixer is lifted by rope traction or mechanical piston tilting device, and when it is overturned again, the mixer can be put down to start mixing; In order to transfer the overturning vehicle from one fermentation pond to another fermentation pond, the track conveyor and crane can be used to scrape out the conveyor and belt conveyor. Feeder or swing conveyor, compost is agitated by mixer, conveyed by vehicle conveyor at the end of fermentation pool, and finally scraped out of the pool by scraper conveyor placed on movable car. Several specific stages of fermentation process are controlled by a compressor, and the required air is blown in from the bottom of fermentation pool.
(3) Crane overturned fermentation tank.
This kind of fermentation tank is usually used for secondary fermentation. The compostable materials which have been crushed and sorted by the pretreatment equipment or which have been fermented once are sent to the fermentation tank by the conveying equipment, and the compostable materials which are fed into the fermentation tank are piled up in the designated box fermentation tank by the shuttle conveying equipment. During accumulation, air is supplied from suction trough, and hopper crane is used to overturn material and perform vaccination operation at the same time.
(4) Horizontal blade fermentation tank
The agitator blade is attached to the mobile device and then moves. Because the mixing device can move horizontally and vertically, the mixing device moves the mixing material repeatedly vertically and transversely at the same time. Because stirring can be used throughout the fermentation tank, the fermentation tank can be designed very wide, so that the fermentation tank has greater processing capacity.
(5) Horizontal scraper fermentation tank.
The main component of the fermentation tank is a flaky scraper driven by gear and rack. The scraper swings from left to right to stir waste, returns from right to left without load, and then swings from left to right to push a certain amount of material. The amount of material pushed by the scraper can be adjusted. For example, when stirring once a day, adjustable push volume is required for a day. If the treatment capacity is large, the fermentation tank can be designed into a multi-stage structure. The pool body is a sealed negative pressure structure, so the odor does not escape. The fermentation tank has many ventilation holes to maintain aerobic condition. In addition, sprinkler and drainage facilities are installed to regulate humidity.
The type of composting equipment used and the corresponding composting process usually depend on the following factors:
- Types of solid waste;
- Establishing natural conditions of composting plant site (distance from residential area, topography, wind direction, etc.);
- Control level of secondary pollutants (leachate, odor gas) in composting process;
Investment and operation cost of plant construction.
Because of the superiority of geographical location, stacking composting can be widely used in rural areas and small towns. However, in some densely populated rural areas, farms, aquaculture farms, urban suburbs and other areas, the composting process with high efficiency for odor gas and leachate treatment should be chosen first.
Trend of development
The Seattle Solid Waste Utilities Bureau first implemented the Masterminer Program in the United States in 1986, marking the beginning of household composting, which mainly uses composting technology to treat yard waste and food waste. In 1995, 41% of Seattle households implemented household composting, diverting about 8 300 tons of yard waste, 82% of which was used for yard greening. There are studies. In the Mississauga area of Ontario, roadside collection, centralized composting and household composting cost $140 t-1, $190 T-1 and $50 t-1, respectively. Moreover, household composting can reduce the amount of household garbage by 3%-5%. Compared with centralized and large-scale composting systems, household composting has significant advantages: low cost and reduction of solid waste sources. In Seattle, there are two types of household composters for food waste: earthworm boxes and conical buckets. In the past, earthworm boxes were commonly used. Now, conical barrels are popular. The height of conical barrels is about 0.9 M. There is a basket with a height of 0.46 M. It can accommodate food waste produced by a family of three within 6 to 9 months. There are two kinds of household composters for yard waste: 0.34 m3 and 0.59 m3. Wood, recycled polyethylene and stainless steel are used to make household composters.
Composting toilets are suitable for places without or without water, such as large-scale composting toilets for parks, highways, stations, etc., and small-scale composting toilets for ships, etc. The commercial composting toilets are divided into self-contained and centralized ones, which can be operated intermittently or continuously, and are made of glass fibre and polyethylene. The self-contained composter is located next to the toilet, while the centralized composter is located next to the basement or building. Intermittent composting toilets contain more than one compartment. When one compartment is full, they are transferred to another compartment. Its advantage is that there is only one compartment in the composting toilet which can run continuously without contamination by fresh manure. Fresh manure and decomposed quasi-manure are mixed together.
Small Capacity Reactor Suitable for Field Operation
Because of the economic, odor control and site reasons, composting systems with large reactors, forced ventilation static stacking and strip stacking are greatly limited. Therefore, a portable, small-capacity reactor composting system suitable for field operation emerges as the times require. For example, Mulch Co. of County, UK, has built two mobile composting systems (30.584-38.23 m3 in volume) similar to rolling containers, with bucket loaders for feeding and cranes for lifting containers when discharging, and materials poured out from the back door of containers. Temperature and oxygen content are controlled by computer. Although this kind of system has only appeared for a few years, it is receiving more and more attention and application from small sewage treatment plants, food industry, catering industry, communities, schools, hospitals, research institutes and business groups. At present, it is mainly used for food waste treatment. The small capacity reactor composting system on the market includes box system, mixing bin and rotary digester, etc. But at present, the most commonly used one is box composting system. The system can be operated intermittently or continuously. It has the advantages of good process control, low investment and operation cost, simple equipment, easy operation and assembly, etc. But its greatest advantage is that it is easy to operate and assemble. Organic waste treatment technology is provided for groups or units that do not have enough space. Currently, 50 and 25 box composting systems are operating in the United States and Canada, respectively. A typical box-type composting system has a treatment scale of 1-40 t/d-1. It consists of several boxes, two of which are used as biofilters. In order to facilitate field operation, the mixing equipment and reactor are connected with the trailer.
In a word, the source of solid waste is more and more dispersed, and the amount of solid waste is also more and more, so the application scope of composting equipment will gradually expand. For different solid wastes, different composting equipments need to be adopted and developed. With the development of solid waste composting, household composters and small-capacity reactor composting systems emerge as the times require. On the one hand, home composters have been reduced from the source.