1. Overview China possesses abundant biomass energy resources, with crop straw resources exceeding 720 million tons, of which 604 million tons are usable for energy. Straw resources represent one of the most promising green renewable energy sources for development and utilization. If these straw resources were used for power generation, it would be equivalent to a 90 million kW thermal power unit operating for an average of 5000 hours per year, generating 450 billion kWh annually. Straw is a low-carbon fuel, with lower sulfur and ash content than the widely used coal, making it a relatively "clean" fuel. Developing straw power generation under effective pollution control measures would significantly improve environmental quality and be highly beneficial for environmental protection. Promoting straw power generation technology in rural areas is of particular importance in saving non-renewable resources and alleviating power supply shortages. 1.1 Market Analysis of Straw Power Generation in China The development and application of biomass straw power generation technology has attracted the attention of governments and scientists worldwide. They all regard biomass straw power generation technology as a key project in their 21st-century renewable energy development strategies. According to the goals set forth in China's Outline for the Development of New Energy and Renewable Energy, by 2010, China's installed capacity of biomass power generation should exceed 3 million kW. Therefore, from the central to local governments, a series of subsidy policies have been formulated to support the development of biomass energy technology, accelerating the process of technology commercialization. With the rapid development of China's national economy and the continuous improvement of the living standards of urban and rural residents, the utilization prospects of straw power generation technology, which has both economic and social benefits and protects the environment, will become increasingly broad. According to a series of preferential policies for renewable energy power generation, the electricity generated by straw power plants is fully purchased by the power grid; the on-grid electricity price, after being submitted to the National Development and Reform Commission for approval by the local provincial government's price authority according to current electricity price policies, is generally around 0.50-0.60 yuan; import duties and import value-added tax on imported equipment are completely exempted. At the same time, various provinces and cities have also formulated other subsidy policies tailored to local conditions. The introduction of these policies has provided strong guarantees for the promotion and utilization of straw power generation in rural areas. It is foreseeable that the market for promoting biomass straw power generation technology in rural China is vast and the prospects are bright. 2. Biomass Straw Power Generation: Straw Combustion Methods: 2.1 Direct Straw Combustion Power Generation: The process of direct straw combustion power generation involves burning biomass with excess air in a boiler. The resulting hot flue gas exchanges heat with the boiler's heat exchange components, producing high-temperature, high-pressure steam that expands in a steam turbine to generate electricity. Direct straw combustion power generation technology is basically mature and has entered the promotion stage. This technology has high efficiency and reasonable unit investment under large-scale conditions; however, due to limitations in raw material supply and process, the power generation scale should not be too large, generally not exceeding 30MW. 2.2 Straw Co-combustion Power Generation: Co-combustion power generation includes: direct co-combustion power generation, indirect co-combustion power generation, and parallel co-combustion power generation, with direct co-combustion power generation being the main application method. Direct co-combustion power generation involves mixing straw fuel with fossil fuels in the same boiler to generate steam, which drives a steam turbine to generate electricity. 2.3 Gasification Power Generation: Gasification power generation involves gasifying straw raw materials in a gasifier to generate combustible gas. After purification, this gas is supplied to an internal combustion engine or a small gas turbine to drive a generator to generate electricity. The scale is generally smaller, mostly not exceeding 6MW. 3. Biomass Straw Power Generation Process 3.1 Straw Processing, Transportation, and Combustion A separate straw warehouse is constructed within the power plant, and the straw's moisture content is tested. Any bale of straw with a moisture content exceeding 25% is considered substandard. In European power plants, this test is performed using infrared sensors installed on automated cranes. In China, a detector can be manually inserted into each straw bale to test the moisture content. This detector can store 99 sets of measurements. After measuring all the straw bales, the results are stored in a computer connected to a weighbridge. Then, a forklift is used to unload the load, 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 unloading, as well as the moisture content. When the truck is unloading, forklifts place the straw bales in pre-determined locations; at the other end of the warehouse, forklifts place the straw bales on the feeding conveyor; the feeding conveyor has a buffer platform that can hold the straw for 5 minutes; the straw is conveyed from the feeding platform through the feeding conveyor with a sealed gate (fireproof) to the feeding system; the straw bales are pushed onto two vertical screws, and the rotation of the screws shreds the straw, then the straw is conveyed to the screw automatic feeder, which presses the straw into the sealed feeding channel, and then conveys it to the furnace bed. The furnace bed is a water-cooled vibrating furnace, which is equipment specifically developed for straw combustion power plants. 3.2 The boiler system adopts a natural circulation drum boiler, with superheaters arranged in two stages in the flue, and an economizer and air preheater arranged at the tail end of the flue. Due to the relatively high alkali metal content in straw ash, the flue gas has high corrosivity at high temperatures (above 450℃). In addition, the fly ash has a low melting point and is prone to slagging. If ash becomes solid or semi-fluid, it is difficult to remove during operation, hindering heat transfer from flue gas to steam in the pipeline. In severe cases, it can even completely block the flue gas passage, trapping flue gas in the boiler. Due to these problems, a superheater system is specifically designed. 3.3 Steam Turbine System The steam turbine and boiler must be consistent in terms of start-up, partial load, and shutdown operations; coordinating the operation of the boiler, steam turbine, and condenser is crucial. 3.4 Environmental Protection System After the wet flue gas purification system, a bag filter is installed to collect fly ash from the flue gas. The emissions from the bag filter are below 25 mg/Nm3, significantly lower than the ash emission levels of coal-fired power plants in China. 3.5 By-products Straw typically contains 3%–5% ash. This ash is collected in the form of boiler fly ash and bottom ash/ash residue. This ash is rich in nutrients such as potassium, magnesium, phosphorus, and calcium, and can be used as a high-efficiency agricultural fertilizer. 4. Introduction to Jiangsu Guoxin Huai'an Chuzhou Biomass Straw Power Generation Project 4.1 Project Overview The Huai'an Chuzhou Straw Power Plant is a power plant jointly invested and constructed by Jiangsu Guoxin Asset Investment Management Group Co., Ltd. and Jiangsu Provincial New Energy Development Co., Ltd. Located in the northwest corner of Zone B of Huai'an Chuzhou Economic Development Zone (a provincial-level economic development zone), the plant site is 500m south of the Xinchang Railway and 650m west of the Beijing-Shanghai Expressway. The installed capacity is 2×15MW units equipped with two 75t/h straw-burning fixed vibrating grate medium-temperature and medium-pressure boilers. The generator sets consist of one 15MW medium-temperature and medium-pressure condensing steam turbine generator set and one 15MW medium-temperature and medium-pressure extraction condensing steam turbine generator set. After completion, the project will consume over 200,000 tons of straw annually, generate approximately 200 million kWh of electricity, generate over 100 million yuan in sales revenue, and nearly 10 million yuan in profits and taxes. The ash residue from straw combustion can be comprehensively utilized. The construction of this project will play a certain role in promoting local economic development, improving rural energy structure, protecting the ecological environment, and developing a circular economy. 4.2 Main Equipment Configuration: Huai'an Chuzhou Straw Power Plant is the first biomass power plant in China to use rice straw as fuel entirely. The boiler is a 75t/h straw-burning fixed vibrating grate medium-temperature and medium-pressure boiler from Wuxi Huaguang Boiler Factory. The steam turbines are one 15MW medium-temperature and medium-pressure condensing steam turbine and one 15MW medium-temperature and medium-pressure extraction condensing steam turbine from Qingdao Jieneng Steam Turbine Factory. Each boiler is equipped with a water-cooled sleeve-type screw conveyor or drum-type ash cooler with a chain bucket conveyor at its bottom to send the boiler bottom ash into the ash bin for loading and transportation. Fly ash collected by bag filters can be directly transported to the plant's ash silo via pipeline using a positive pressure dense-phase pneumatic centralized system, eliminating intermediate links. The ash silo has a capacity of 600 m³, sufficient to store one week's worth of ash. To better meet comprehensive utilization requirements, the ash silo has two unloading methods: one is loading into tank trucks by a dry bulk loader for dry ash users; the other is a wet mixer where dry ash is moistened with water before loading and transportation. Dust is removed using high-efficiency bag filters with a dust removal efficiency of 99.99%. Domestic sewage is treated by an underground sewage treatment system and then used for greening the factory area; circulating water discharge is partially recycled for ash conditioning, hydraulic slag removal, and miscellaneous water use in the main plant, with the remaining water discharged into the Chuzhou Development Zone Sewage Treatment Plant; boiler discharge is mixed with excess circulating discharge and then discharged into the Chuzhou Development Zone Sewage Treatment Plant; chemical acid and alkali wastewater is neutralized and treated to meet standards before being discharged into the Chuzhou Development Zone Sewage Treatment Plant. Main Equipment List Item No. Equipment Name Manufacturer 1 Boiler Wuxi Huaguang Boiler Factory 2 Steam Turbine Qingdao Jieneng Steam Turbine Factory 2 Chain Plate Zhangjiagang Free Trade Zone Fangyuan Machinery Co., Ltd. 2 Crusher Yixing Julong Environmental Protection Equipment Factory 2 Large Inclined Angle Belt Zhangjiagang Free Trade Zone Fangyuan Machinery Co., Ltd. 2 Material Distributing Screw Conveyor Shandong Shankuang Machinery Co., Ltd. 2 Feeding Screw Conveyor Boiler Factory Self-Provided 4.3 Feeding and Combustion System Equipment and Process Flow Since the boiler mainly uses soft straw, its fuel conveying and combustion system differs from that of conventional power plants. The straw used in the power plant is transported by road; one straw storage silo is provided, with an effective area of ​​approximately 4,000 m2 and a volume greater than 50,000 m3. The straw warehouse adopts a frame structure formed by cast-in-place reinforced concrete columns and steel roof trusses. The straw needs to be stacked neatly for easy operation of the grab bucket crane. The straw packaging dimensions for Chuzhou straw power generation are required to be 1700x1000x900 (length x height x width) (mm); the density of the straw bales is 250 kg/m3. The straw bales need to be manually unpacked before entering the crusher. To prevent blockage and friction-induced fires, the straw bales must not contain soil, wire, iron blocks, or other debris. Straw entry process into the furnace: A1 Transition chain conveyor → A2 Feeding chain conveyor → A Crusher 1A Subcontracting Platform B1 Transition chain conveyor → B2 Feeding chain conveyor → B Crusher Grab Bucket High-Angle Belt → C1 Transition chain conveyor → C2 Feeding chain conveyor → C Crusher 1B Subcontracting Platform D1 Transition chain conveyor → D2 Feeding chain conveyor → D Crusher A1, A2, A3 Distribution screw conveyors → A1, A2 Feeding screw conveyors hopper furnace B1, B2, B3 Distribution screw conveyors → B1, B2 Feeding screw conveyors The grab bucket and subcontracting platform are provided and controlled by the Beijing Lifting and Transportation Machinery Research Institute. The equipment after the subcontracting platform is controlled by DCS. There is an interface between DCS and the subcontracting platform. The hard-wired signals for a single furnace and a single set of conveyors are as follows:  DCS to subcontracting platform: Discharge command, fault shutdown;  From the subcontracting platform to the DCS: The grab bucket machine grabs straw bales from the warehouse and places them on the subcontracting platform. Simultaneously, the subcontracting platform distributes bales to the two subsequent transition chain plates, distributing 5 bales to each plate at a time. After all the straw bales from the two transition chain plates are delivered to the feeding chain plate, the DCS sends a material signal to the subcontracting platform. Upon receiving this instruction, the subcontracting platform distributes the bales to the transition chain plates. The subcontracting speed of the subcontracting platform is adjustable from 3 to 10 meters per minute. Each furnace has two sets of chain plate conveyor lines. Each chain plate conveyor line includes two transition chain plate conveyors after the subcontracting platform and two feeding chain plates. Each feeding chain plate corresponds to one crusher. Each furnace has a total of 8 chain plates and 4 crushers. The chain plates are supplied by Zhangjiagang Free Trade Zone Fangyuan Machinery Co., Ltd., and the crushers are supplied by Yixing Julong Environmental Protection Equipment Factory. The speed of the transition chain plate is adjustable from 0.5 to 5 meters per minute. Each transition chain plate is equipped with three material sensors (one each at the front, middle, and rear) (photoelectric or mechanical detection devices). When all three sensors detect no material, the DCS considers the transition chain plate to be empty. The transition chain plate has a straw bale correction function. The normal speed of the feeding chain plate is 0.6 meters per minute (power frequency speed), with a maximum of 0.84 meters per minute. The maximum bale feeding speed of the crusher is 0.84 meters per minute. The speed of the feeding chain plate and the crusher must be matched. Therefore, the speed of the feeding chain plate is generally lower than the maximum crushing speed of the crusher. When the crusher has high resistance, the transition chain plate and the feeding chain plate automatically reverse simultaneously to protect the crusher. The feeding system is the core of the straw power plant, and the crusher is the core of the entire feeding system and also one of the largest electrical equipment in the straw power plant. The operation of the crusher directly affects the operation and efficiency of the straw power plant. Each crusher is divided into a crushing section and a chopping section. The crushing section includes a lower main crusher (132kW) and an upper auxiliary crusher (75kW); the chopping section includes three chopping motors (5kW each). The crusher feed inlet size is 1200 x 1000 mm. Straw bales enter the crusher from the feeding chain and are first crushed by two crushers, then further chopped by three choppers located below the crushers, resulting in straw fragments approximately 3-5 cm long for boiler combustion. A single chain conveyor crushing line is considered operational only when all equipment (including one sub-bundling platform, two transition chains, two feeding chains, and two crushers) is functioning normally. A fault in any piece of equipment on a single chain conveyor crushing line indicates a fault in that line. During normal operation, the two chain conveyor crushing lines serve as backups for each other. If one line fails, the other line must be started immediately; if both lines fail, the boiler must be shut down. The feed chain plate rotates at the same speed as the crusher. The transition chain plate rotates at the same speed as the distribution platform during subcontracting, and slightly higher after subcontracting. The steep-angle belt is supplied by Zhangjiagang Free Trade Zone Fangyuan Machinery Co., Ltd., the distribution screw conveyor by Shandong Shankuang Machinery Co., Ltd., and the feeding screw conveyor by the boiler plant. The steep-angle belt is approximately 150 meters long. Material from the crusher falls onto the belt and is transported for 150 meters before entering the silo. The straw silo is generally used only for transfer and distribution and not for storing straw fuel. The silo design of the Chuzhou project automatically and evenly distributes straw to both sides of the silo via upper baffles to ensure that the screw conveyors on both sides provide fuel evenly to the furnace. Fuel from the silo first passes through the distribution screw and then the feeding screw before entering the boiler. A fire door is installed between the distribution screw and the feeding screw to ensure the safety of the silo. The Chuzhou straw power plant has two screw conveyor lines. To ensure uniform heating of the furnace during combustion, both lines are generally required to feed simultaneously. The feeding screw conveyor is located at the bottom of the hopper. Each feeding screw conveyor consists of three screws, each controlled by a frequency converter for start-stop operation. Differential speed operation is possible when needed. It has independent start-stop functionality on-site. Each feeding screw consists of two screws, each controlled by a frequency converter. The feeding screws can operate at differential speeds. Fuel falls into the furnace for combustion after passing through the two-stage screw conveyor. The air and flue systems are similar to traditional circulating fluidized bed furnaces. The system is equipped with one forced draft fan, one secondary air fan, and one induced draft fan. The secondary air duct is connected to the superheated primary air duct after the air preheater. Primary air blows fuel up from below the furnace bed, while secondary air enters at the waist of the furnace to aid combustion. 4.4 Control System Configuration The control system's scope includes the feeding system, boiler, turbine, generator, and utility systems. The entire DCS system has nearly 4000 points. The DCS system controller configuration is as follows: The boiler has 4 pairs of controllers: 1 pair for the steam-water and FSSS systems, 1 pair for the flue gas system, 1 pair for the feeding system, and 1 pair for the bag filter and other boiler systems; the turbine has 2 pairs of controllers: 1 pair for the main steam high and low pressure heaters, and 1 pair for the oil system #1 plant power supply; a total of 3 pairs of controllers for the public and electrical systems. The human-machine interface configuration includes 6 operators, 1 shift supervisor station, and 1 engineer station. The main normal operating parameters of the boiler are: main steam pressure 3.45 MPa, main steam temperature 450℃, and flue gas temperature at the furnace outlet 270℃. 4.5 Challenges of Straw Power Plants As the first (and possibly the world's first) biomass power plant in China using soft straw (rice straw) as fuel, Jiangsu Guoxin Huai'an Biomass Power Plant encountered many difficulties during commissioning and trial operation. The calorific value of straw is only half that of coal; for the same 75-ton boiler, the weight of straw alone must be twice that of coal fed into the furnace. The straw silo only serves as a transfer point and does not have a storage function. Ensuring continuous operation with so much straw continuously passing through the crusher and screw conveyor into the furnace is a challenge. Rice straw is relatively soft and needs to be crushed to a length of 4-5cm to prevent it from tangling on the screw conveyor. However, in practice, due to the messy baling of straw, the crusher struggles to break it to this length. Therefore, the Chuzhou straw power plant plans to install a chopping motor under the crusher to further improve the straw crushing effect. Combustion control is another challenge. Controlling the furnace temperature and pressure is difficult. Rice straw is very light; even a slight increase in airflow or a decrease in feed rate will cause the straw to fly around, resulting in temperature fluctuations in the furnace. To improve combustion, a suitable proportion of peanut shells can be added to the fuel. Peanut shells are heavier than rice straw and help improve combustion and reduce screw blockage. The peanut shells can also help the rice straw settle on the furnace bed, stabilizing combustion. It can be said that solving the feeding system problem will allow the straw power plant to operate successfully. 4.6 Prospects for Straw Power Plants If properly established, straw power plants have a bright future. Nationally, the government strongly encourages the use of green and renewable energy, and straw power plants, using straw as fuel, receive strong government support. For the next 15 years, the government will provide a subsidy of 0.25 yuan per kilowatt-hour of electricity. my country is a major agricultural country; directly burning straw in farmland is wasteful of resources and causes air pollution, interfering with highways and aircraft takeoffs and landings. Therefore, the government has explicitly prohibited the burning of straw in farmland. From a raw material perspective, straw power plants have an inexhaustible supply of fuel. In Chuzhou, straw within a 90-kilometer radius can meet the operating needs of the Chuzhou straw power plant. Furthermore, straw power plants address farmers' straw problem and increase their income. The ash residue from the plant has low ash content, making it an excellent fertilizer that can be sold to farmers for reuse. Straw power plants are green and pollution-free power plants. 4.7 Unit Operation Status From 14:30 on November 5, 2007 to 14:30 on November 9, 2007, Unit #1 of Jiangsu Guoxin Huaian Biomass Power Generation Co., Ltd. successfully passed the 72+24 hour trial operation, and the first generator unit in China using rice straw as fuel was successfully put into commercial operation.