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Energy-saving, consumption-reducing and emission-cutting renovation of circulating fluidized bed boilers – Lu Bing (Tangshan Zhongrun Coal Chemical Co., Ltd.) 【Abstract】 For the 2.2 million t/a coking project of Tangshan Zhongrun Coal Chemical Co., Ltd., there are four 35-t boiler units installed as part of the first phase of this project, which has a capacity of 1.1 million t/a in coking. Boiler No. 3 is of the TG-35/3.82-MQJ type, with an evaporation capacity of 35 t/h and a pressure of 3.82 MPa; it uses a mixture of coal and gas as fuel. The boilers originally designed for a 70% coal + 30% coke oven gas or washed middling combustion configuration were modified into boilers that burn 100% coke oven gas. 【Keywords】 TG-35/3.82-MQJ boiler renovation, TG-35/3.82-Q1. Existing work foundation, features, and advantages: Circulating fluidized bed boilers belong to the category of boiling boilers. It is a new type of combustion device whose combustion mode lies between stratified combustion and suspended combustion. The fuel is in a boiling state inside the furnace, just like boiling water. To improve boiler efficiency, primary return and secondary return were designed. Circulating fluidization gets its name from this. The TG-35/3.82-MQJ circulating fluidized bed gas-coal hybrid boiler has a rated steam temperature of 450°C and a design efficiency of 89%. The particle size range of the limestone used for desulfurization is 0–1 mm, with a desulfurization efficiency of 80%. The motor power of the primary fan is 220 KW. It can burn low-quality fuels such as stone coal and coal gangue, which cannot be burned using conventional combustion methods. It has a wide range of adaptability to changes in load. By feeding the absorbent (limestone, dolomite) together with coal particles into the fluidized bed for combustion, it is possible to **reduce the SO2 content in the flue gases, thereby minimizing air pollution as well as reducing corrosion of the boiler’s heating surfaces ； The temperature in the fluidized bed is low, so the content of nitrogen oxides (NOx) in the flue gas is low, which is beneficial for environmental protection ； Due to the low combustion temperature, it is not easy to disrupt the mineral structure in the ash, and the low carbon content in the slag facilitates the comprehensive utilization of the ash. 2. Reasons for initiating the project, implementation schedule, and safeguard measures: Since coke ovens No. 4 and No. 3 came online in October 2006 and January 2007 respectively, while the first-phase project for producing methanol from gas at a capacity of 100,000 tons per year was still in progress, the gas produced by these coke ovens was vented at a rate of about 20,000 m3/h. This not only required a significant amount of labor but also resulted in substantial resource waste. Therefore, it was decided to convert Boiler No. 3 into a boiler that burns gas exclusively; no major changes to its structure will be made, and it can be reverted to its original mixed-fuel operation mode when necessary. After this conversion, a large amount of coal resources can be saved, the utilization efficiency of gas can be improved, gas emissions can be reduced, the environment can be protected, energy consumption can be lowered, and as a result, significant financial savings can be achieved. 3. The implementation schedule is as follows: 3.1 From January 1 to February 10, 2007, the production of modified components, their installation, as well as the procurement and installation of materials and equipment. 3.2 February 11–20, 2007: Insulation of the boiler furnace wall. 3.3 From February 21 to March 10, 2007, overall boiler commissioning. 4. The guarantee measures are as follows: 4.1 Boiler body: Remove the original fluidized bed air boxes, air distribution plates, and air nozzles, and reinstall support plates to fix the burners ； Place a burner at the original air distribution plate location ； An explosion-proof door is installed on each side of the furnace outlet, and the corresponding fins are removed ； The original return material container area is covered with fine ash to protect the return air duct. 4.2 Gas and air distribution pipeline system: Redo the fabrication and installation of this gas and air distribution system ； Adjustable dampers were fabricated and installed separately for the secondary air ducts at the 8500 mm elevation of the original boiler ； Install 8 flame monitors on the 8 burners at a height of 6800 mm on the original boiler. 4.3 Auxiliary equipment: The original blower was a high-pressure blower for circulating fluidized beds, with relatively high specifications; therefore, a blower that matches these specifications needs to be replaced. Blower model: Type 9-26, No14D, 110KW. 4.4 Electrical control: Add electrical control requirements for this section. 5. Calculation of cost savings: The cost of thermal coal is 200 yuan per ton. One boiler consumes 4.2×24 = 100.8 tons per day; over 365 days in a year, the total amount of thermal coal consumed is 200×100.8×365 = 7.3584 million yuan. The original blower motor had a power rating of 220 KW, while after the modification it was 110 KW. The daily electricity consumption is divided into three periods: the peak period costs 0.6137 yuan per kilowatt-hour, the off-peak period costs 0.2577 yuan per kilowatt-hour, and the average period costs 0.4197 yuan per kilowatt-hour. Calculating for all 365 days of the year, the total amount saved in electricity costs is: (0.6137 + 0.2577 + 0.4197) × 8 × (220 – 110) × 365 = 414,701.32 yuan. The total cost for power consumption, labor costs, and equipment maintenance in the coal feeding system is approximately 500,000 yuan. The total amount saved throughout the year was 735.84 + 41.470132 + 50 = 827.310132 million yuan. Note: Gas consumption is not taken into account due to the combustion and release of excess gas. 6. Energy calculation: Note: The calorific value of thermal coal is 3000 kcal/kg, while that of coke oven gas is 17,000 kJ/m3. Before the renovation, 4.2 t/h of thermal coal and 3500 m3/h of coke oven gas were consumed; thus, the energy consumption per hour before the renovation was 4.2×1000×3000×4.18 + 3500×17000 ≈ 1.1×108 kj. After switching to a pure coke oven gas combustion mode, 6500 m3/h of coke oven gas is consumed, resulting in an energy consumption of 6500×17000≈1.1×108 kj per hour. Energy consumption remains essentially unchanged before and after the renovation.