In the horizontal tube continuous cooking system, the spray bin (also known as the spray tank or discharge bin) is the last key equipment of the cooking process, which is mainly used for rapid pressure relief, cooling and preliminary separation of the pulp after cooking. Its core role is to safely and efficiently handle high temperature and high pressure pulp, and provide suitable conditions for subsequent processes (such as washing, screening). The following are the specific functions of the spray bin:
1. Fast pressure relief and flash evaporation
● The cooked pulp enters the spray bin at high temperature and high pressure. By suddenly lowering the pressure (such as from 1.2MPa to normal pressure), the water in the pulp is rapidly evaporated (flash evaporation), reducing the pulp temperature and releasing residual steam.
● Example: In sulfate pulping, the temperature of the pulp at the outlet of the cooking tube is about 170℃ which is reduced to below 100℃ after being relieved by the spray bin.
2. Pulp cooling and stabilization
● The temperature of the pulp is further reduced by the cooling device in the spray bin (such as spray water) or natural heat dissipation to avoid damage to the subsequent equipment (such as pumps and pipes) caused by the high temperature pulp.
● Example: In the production of straw pulp, the spray bin cools the pulp to below 80℃ for subsequent washing and screening.
3. Steam Recovery and Energy Utilization
● The high-temperature steam released by the spray bin can be used to preheat clean water or cooking chemical solutions through the waste heat recovery system (such as heat exchanger), reducing the energy consumption of the system.
● Example: In a large pulp plant, the steam recovery of the spray bin can meet 20% to 30% of the heat demand for the process.
4. Preliminary separation of pulp and black liquor
● The cooked pulp contains a large amount of black liquor (lignin, residual chemical solutions, etc.). The spray bin is separated by gravity sedimentation or centrifugation to achieve the preliminary separation of pulp and black liquor.
● Example: In KP pulping, the black liquor is discharged at the bottom of the spray bin, and the pulp is output at the upper part, which is convenient for subsequent black liquor evaporation and pulp washing.
5. Safe pressure relief and system protection
● The spray bin is equipped with a safety valve or bursting disc to prevent equipment overpressure damage due to poor pressure relief and ensure the safe operation of the system.
● Example: When the pressure of the cooking tube is abnormally increased, the spray bin can quickly relieve pressure to avoid the risk of equipment explosion.
