0 Overview The No. 1 to No. 3 boilers at the Daqing Oilfield Thermal Power Plant are HG-670/13.7-HM12 solid slag discharge pulverized coal boilers manufactured by Harbin Boiler Factory. They were put into commercial operation in November 1991, November 1992, and September 1993, respectively. The original design used a siphon-type water flushing slag removal system. Coke lumps were crushed by a single-tooth roller slag crusher and fell into the ash ditch, where they were flushed away by pressurized water. Since its commissioning, the unit has mainly experienced the following problems: a. The sealing water tank has lost its sealing function. During operation, the sealing water tank fills with coke lumps, and as the furnace bottom expands outwards, it damages the water tank, preventing water injection. b. The four slag removal doors at the furnace bottom are normally open, creating major air leakage points in the boiler. c. The ash spraying nozzles in the ash hopper are all internally installed and repairable structures, making them impossible to repair during operation. Damage to these nozzles renders them ineffective for ash spraying. d. Many safety hazards exist during the operation of this unit. When the coke volume is large, ash removal personnel are required to clear the blockage, which often results in hot coke lumps spraying out and scalding personnel, seriously affecting civilized production on site; moreover, ash water can easily cause burnout accidents to the motor of the slag crusher. Based on the above problems, during the overhaul of No. 2 boiler in May 1997 and No. 3 boiler in May 1998, a safe, efficient and reliable spiral slag remover was selected to replace the siphon-type open water flushing slag removal device. This solved the above problems. [b]1 Principle and Application of the New Spiral Slag Remover[/b] 1.1 Principle of the Spiral Slag Remover The LCSZ-7.5 spiral slag remover consists of two parts: a spiral slag remover and a slag crusher. The spiral slag remover is composed of a motor, a reducer, a spiral main shaft, etc.; the slag crusher is composed of a motor, a reducer, a slag crushing rotor, etc. Its working principle: The slag produced after the pulverized coal combustion in the furnace falls along the water-cooled wall into the ash trough of the spiral slag remover filled with cold water due to its own weight. It is quenched and cooled by the water, breaking into small pieces. These pieces are then lifted by the spiral shaft out of the water to the outlet of the ash removal trough, where they are crushed by the slag crusher and fall into the ash ditch, where they are flushed away by pressurized water. The entire furnace bottom is submerged in the ash trough filled with cold water. The slag removal is automatically completed in a closed mechanical system, thus completely eliminating air leakage at the furnace bottom. Since no workers are required to clean the ash, there is no risk of burns to workers. The ash spray nozzles of this device adopt an insert-type external mounting and repair structure, facilitating inspection and maintenance. 1.2 Installation of the new slag remover: Remove the original slag removal device, reopen the ash ditch, install ground anchors and tracks, install the prefabricated ash hopper and single-wave compensator on the lower header of the water-cooled wall, and then install the slag remover and slag crusher in place. [b]2 Application Effect Analysis[/b] The original slag removal device suffered from severe air leakage at the furnace bottom, causing the flame center to shift upwards, resulting in higher flue gas temperatures and increased coking inside the furnace, which significantly impacted boiler efficiency. After replacing it with a new spiral slag removal device, the air leakage at the furnace bottom was eliminated, reducing the leakage from 76×10⁴ m³/h to zero, lowering the flue gas temperature by 8–10°C, greatly alleviating coking inside the furnace, and improving boiler efficiency. Now, taking Boiler No. 3 as an example, we will analyze the energy-saving effect solely from the perspective of the reduction in flue gas temperature. After the slag removal device was put into operation in Boiler No. 3, the average flue gas temperature decreased by 8℃. The total ventilation volume of the boiler was 1.25×10⁶ m³/h. Assuming an annual equivalent availability factor of 5000h, the equivalent coal-saving benefits are as follows: Coal saved: M1; Fuel calorific value: Q = 1.33×10⁴ kJ/kg; Flue gas enthalpy difference: HP = 12 kJ/kg; Boiler flue gas volume: P = 1.25×10⁶ m³/h; Therefore, M1×Q = HP×P = 1.3 t/h. The annual coal saved is 1.3×5000 = 6500 t (equivalent to a value of 975,000 yuan). The social benefits are significantly improved. [b]3. Issues to be noted during on-site use[/b] a. In the initial stage of boiler ignition, it is difficult to clean the slag oil that falls into the slag remover. Therefore, on the one hand, the quality of oil gun maintenance should be improved to prevent oil from splashing out of the oil gun; on the other hand, the slag remover should be pulled out and placed in the maintenance position in the initial stage of ignition, and then returned to its original position after coal feeding. b. When metal debris falls into the slag remover, it will cause the auger shaft to jam, increasing the workload of maintenance. Therefore, the manhole doors and inspection holes of the boiler body should be sealed to prevent the throwing of debris. c. Try to avoid coke and oil mixing and distribute air reasonably. If a large amount of coke falls into the slag remover and jams or buries it, measures should be taken to cut off the power, clean the ash, rotate the machine, restore power, and put it into operation.