In the horizontal tube continuous cooking system, the vertical unloader (also known as vertical unloading valve or vertical discharge device) is a key equipment, mainly used for unloading, cooling and pressure control of the pulp after cooking. Its core function is to safely and efficiently discharge the high temperature and high pressure pulp from the cooking pipe, and provide suitable conditions for subsequent processes (such as washing and screening). The following is the specific functions:
1. Safe unloading and pressure control
● The cooked pulp enters the vertical unloader under high temperature and high pressure, and the pressure is reduced from the high pressure of the cooking pipe (such as 1.2 MPa) to normal pressure through a step-by-step pressure relief device (such as a cone valve or a multi-stage pressure relief chamber) to ensure the safe and controllable unloading process. ● Example: In sulfate pulping, the vertical unloader gradually reduces the pulp pressure from 1.2 MPa to normal pressure to avoid sudden pressure relief resulting in equipment damage or pulp splashing.
2. Pulp cooling
● Through the cooling device in the unloader (such as spray water or cooling jacket) or natural heat dissipation, the temperature of the pulp is reduced to avoid damage to the subsequent equipment (such as pumps, pipelines) caused by the high temperature pulp.
● Example: In the production of straw pulp, the vertical unloader reduces the temperature of the pulp from 170 ° C to below 80 ° C, which is convenient for subsequent washing and screening.
3. Preliminary separation of the pulp from the black liquor
● The cooked pulp contains a large amount of black liquid (lignin, residual liquid, etc.). The vertical unloader is separated by gravity sedimentation or centrifugation to achieve the preliminary separation of the pulp and the black liquid.
● Example: In KP pulping, the bottom of the vertical unloader discharges black liquor, and the upper part outputs pulp, which is convenient for subsequent black liquor evaporation and pulp washing.
4. Prevent return and blockage
● Through special structural design (such as conical valve or rotating blade), the reverse flow of pulp is prevented or the unloading port is blocked, and the continuous operation of the system is guaranteed.
● Example: In wood chip cooking, the rotating blade of the vertical unloader prevents fiber winding from causing blockage.
5. Automation Control
● Through sensors (such as pressure, temperature) and PLC control system, the automatic operation of the unloading process is realized, and the production efficiency and safety are improved. Example: When the pressure of the cooking tube rises abnormally, the vertical unloader automatically starts the pressure relief program to avoid overpressure damage to the equipment.
