Straw power generation project

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1 Water/Steam Cycle Fossil fuel power generation technology represented by coal has achieved rapid development in recent years. In order to improve the power generation efficiency of the entire power plant, the temperature and pressure of steam have been greatly increased. Great progress has also been made in straw burning power generation equipment. However, compared with coal-fired equipment, there is relatively little experience in the design and construction of straw-fired power generation equipment. And straw also has unique characteristics that make it difficult to achieve higher steam parameters. In particular, the high chloride content in straw increases the possibility of boiler corrosion under high steam pressure. 　　At present, the power generation efficiency of most straw-burning power plants can only reach about 30%. Generally speaking, straw power plants provide heat while generating electricity to improve the efficiency of the entire power plant. %~8 ] ) Each warehouse has a gate, and transport trucks can drive in through the gate and then stop on the weighbridge to weigh the straw. The moisture content of the straw must also be tested. Any package of straw with a moisture content exceeding 25% is deemed unqualified. In European power plants, this test is carried out by infrared sensors mounted on automatic cranes. In China, a detector can be manually inserted into each straw bale to test for moisture. The detector can store 99 sets of measurement values. After measuring all straw bales, the measurement results can be stored in a computer connected to the floor scale. The goods are then unloaded using a forklift and the empty weight of the transport truck is entered into the computer. The computer can calculate the net weight of the straw based on the weight before and after and the moisture content. When the truck is unloading, the forklift places the straw bales into a predetermined location ； At the other end of the warehouse, a forklift places straw bales on a feed conveyor ； The feeding conveyor has a buffer table that can retain straw for 5 minutes ； Straw is transferred from the feeding table to the feeding system through a feeding conveyor with a sealed gate (fireproof) ； The straw bales are pushed onto two vertical screws, and the straw is broken into pieces by the rotation of the screws. The straw is then transferred to the screw automatic feeder, and the straw is pressed into the sealed feeding channel through the feeder, and then reaches the hearth. The hearth is a water-cooled vibrating hearth, which is equipment specially developed for straw burning power plants. K6 e2 L9 S H. U5 i# S7 z 3 Boiler system The boiler adopts a natural circulation drum boiler. The superheater is arranged in the flue in two stages, and an economizer and an air preheater are arranged at the end of the flue. Since the content of alkali metals in straw ash is relatively high, the flue gas is highly corrosive at high temperatures (above 450°C). In addition, fly ash has a low melting point and is prone to slagging problems. If the ash becomes solid and semi-fluid, it will be difficult to remove during operation and will hinder the heat transfer from flue gas to steam in the pipe. In severe cases, it may even completely block the flue gas channel and block the flue gas in the boiler. Because of these problems, specially designed superheater systems are already used in the latest power plants. 4 i) f# u3 a1 x3 ~2 m3 G- u 4 Steam turbine system X' I- P& n 4.2 Air-cooled condenser All power plants in Denmark are seawater cooled, the Sanguesa power plant in Spain is cooled by river water, and the Ely power plant in the UK is equipped with air condensers. In China, air condenser is a very mature product and can be used in straw power plants. ) M1 Q; k! t0 }- C& V; ~. q 5 Environmental protection system 3 C# p' G4 d8 t G 5.1 Bag dust collector After the wet flue gas purification system, a bag dust collector is installed to collect fly ash in the flue gas. The emission of bag dust collector is less than 25 mg/Nm3, * * Lower soot emission levels than coal-fired power plants in China. The bag dust collector is of the pulse jet type, and the container is cleaned by pulses of compressed air. 4 Z: o- M, J& @ 6 By-products + d& y5 c3 M. a$ W0 `& x * b; { Straw usually contains 3-5% ash. This ash is collected in the form of boiler fly ash and ash/bottom ash. This ash is rich in nutrients such as potassium, magnesium, phosphorus and calcium and can be used as an efficient agricultural fertilizer&C o) Q0 p/ Y' p * V6 W0 c 3 Fuel preparation and transportation for straw power generation - m% N3 g4 T; M Straw power generation is a power generation method using straw as the main fuel. It is divided into straw gasification power generation and straw combustion power generation. Straw gasification power generation involves burning straw in an oxygen-deficient state, causing a chemical reaction to generate high-grade, easy-to-transport, and highly-utilized gas, which is then used to generate electricity. Straw combustion power generation is to send straw directly to the boiler for combustion, and then generate steam to drive the generator to generate electricity, which is similar to conventional thermal power generation. However, straw combustion power generation is different from conventional thermal power generation. The biggest difference lies in the preparation and storage of fuel. B, h. R5 y Y5 Z7 @" The fuel for thermal power generation is generally coal. Depending on the boiler, pulverized coal, medium coal and coal gangue are used. Conventional fuel preparation processes include screening, crushing, coal grinding, and transportation. Coal is stored in loose volumes. ' M1Y# _6 r, F4 T' k( } Crop straw is large in volume and fluffy in structure, and must be dried and bundled for storage. There are many ways to put straw into the furnace. You can pack the straw and transport it into the furnace. You can also grind the straw into granules (briquet) and put it into the furnace, or mix it with other fuels and put it into the furnace together. Crushing and granulation has the highest production cost, but the most adaptable. The cost is the lowest when the straw is packed into a furnace for combustion, but the lignin content in the straw has different requirements for the boiler and the adaptability is poor. The straw packaging and transportation process generally uses a forklift to place the straw bags into a predetermined position, and then the forklift places the straw bags on the feed conveyor. The feed conveyor has a buffer table that can retain the straw 5 min, the straw is sent from the feeding table to the boiler feeding system through a feeding conveyor with a sealed gate (fireproof). The straw bales are pressed onto two vertical screw stalks. Through the rotation of the screw stalks, the straw is broken into pieces, and then the straw is transferred to the spiral automatic feeder. The feeder presses the straw into the sealed feeding channel, and then reaches the furnace bed. The hearth is a water-cooled vibrating hearth or a chain grate boiler, which is equipment specially developed for straw burning to generate electricity. Straw boilers do not have a furnace front chamber, so regardless of the installed capacity, the conveying system must be two-way or more. ' a# i$ f( j2 y1 A9 p. S 4 The importance of straw power generation (1) The amount of crop straw is large, the coverage is wide, and the fuel source is sufficient. In particular, photosynthesis during crop growth absorbs CO2, which is balanced with the CO2 generated by burning crop straw. This has a direct effect on reducing greenhouse gas emissions and implementing the "Kyoto Protocol." (2) Since the sulfur content of straw is very low and low-temperature combustion produces less nitrogen oxides, the flue gas after dust removal is no longer desulfurized, and the flue gas can be directly discharged into the atmosphere through the chimney. The flue is equipped with an online detection device for flue gas components for monitoring. Denmark etc. * * The operation test also shows that the flue gas after dust removal from the straw boiler can fully meet environmental protection requirements without adding other purification measures. (3) The calorific value of wheat straw and corn straw is the smallest among crop straws, but the low calorific value is about 14.4 MJ/kg, which is equivalent to 0.492kg of standard coal. Using straw to generate electricity can reduce coal consumption. 2s+O8u- ] 3 \: F- } (4) The ash residue after burning straw is a good potassium fertilizer, which can be directly utilized by crops or deeply processed into compound fertilizer. (5) As a fuel, coal mining has certain risks, especially underground mining, which makes management difficult. Compared with crop straw, it is less dangerous, easier to manage, and is a waste utilization, which is in line with * * Energy development industrial policy.