How to promote the profit of paper pulp production line? Except for the paper pulp machines, paper pulp plant design, there are many other factors affect the profit of paper pulp production, for example, heat recovery is a considerable element for paper pulp plant promotion. Generally, a large amount of heat will be produced during the paper pulp production, there is no heat recovery equipment that will result in a big loss. A reasonable paper pulp plant is absolutely equipped with the heat recovery system.
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The heat recovery of paper pulp making can be divided into two types. The heat recovery method is mainly up to the scale of paper pulp production, pulp load or other factors.
- The heat exchange between dirty steam produced by disc refiner and water in the jet condenser produces the hot water;
- Use reboiler exchange heat between dirty steam and hot condensed water, and produce steam and hot water.
During the high-concentration refining process, in the high-speed rotating disc refiner, about 85%-90% of the motor shaft power becomes thermal energy due to the intense friction between the chips, fibers, or grinding disc, evaporation, which cook the water in the dilution water, water-sealed water, wood chips or fibers generates a large amount of steam, the steam is discharged in the form of reflux steam (counter flow direction with wood chips) and spray steam (discharged with disc pulp). A part of the reflux steam is used to steam the depressurized wood chips, and the remaining part is sprayed to the condenser or combined with the discharge steam to the reboiler to produce fresh steam; the sprayed steam is separated by the pressure pulp separator and then enters the heat recovery system.
The heat recovery system design can be automatically controlled to the corresponding heat recovery equipment based on the need for fresh steam and hot water in production. The amount of steam produced by the refining process is determined by the input of electrical energy, the pressure of the disc grinding, the temperature and water content of the chips, the flow and temperature of the dilution water, the flow and temperature of the water-sealed water, and etc. Purified fresh steam capacity is determined by the boiler feedwater temperature, the discharged amount of soluble solids, and the amount of non-condensate, etc.
Heat recovery process
The heat recovery process for fresh steam production mainly includes several units such as water supply heating, steam generation and hot water production.
- The dirty steam separated by the pulp separator enters the reboiler (also known as the regeneration boiler or flasher) by pressure, and simultaneously supplies water to the boiler of about 100 °C after heat exchange, and the steam Indirect exchange heat with hot water, the dirty steam is cooled until it condenses into condensed water, the cleaned hot-water is converted into steam, and the saturated steam having a dryness of about 99.5% is generated by the embedded droplet separator.
- The clean steam is sent to a steam compressor to be pressurized to a pressure of about 0.5 MPa and sent to a steam point, or the fresh steam is sent directly to the steam point without being pressurized. The reboiler steam has an emptying rate of 1.3%, which contains about 0.1% non-condensable gas (NCG). The amount of NCG will affect the heat transfer coefficient and the emptying rate of the heat recovery unit. The output of fresh steam also depends on the output.
- The condensed water condensed in the reboiler enters from the bottom of the jet condenser and produces flash steam, while clean white water is added from the top of the condenser to the reverse flow of the rising steam to exchange heat to produce clean hot-water and dirty condensate. The clean hot-water is about 70 ° C, and sent to the pulping system or other hot water points by the hot water pump; the condensed dirty condensate is about 100°C, and sent to the chip washing system or pulp washing.
- To prevent the fiber from being precipitated in the reboiler during production, the dirty condensed water is continuously circulated by the circulation pump, and the uncondensed steam and some non-condensable gas are led to the water supply preheater through the top of the reboiler. The condensate from the heat exchange process flows from the bottom of the preheater into the reboiler steam flash zone, and the uncondensed steam (which includes turpentine, some air, and steam, etc.) enters the jet condenser. The cleaning warm water in the boiler is controlled by the liquid level controller, first, pass the heat exchanger, and then through the preheater before the reboiler to reheat and then enter the reboiler.
The heat recovery system usually consists of the heat exchanger, reboiler, jet condenser, and steam compressor, etc.
The reboiler is the core equipment of the heat recovery system, generally introduced from advanced technology. The reboiler is used to exchange most of the dirty steam into condensate water, and the clean condensate water is changed into saturated steam.
The heat exchanger is used as auxiliary heating equipment of the heat recovery system. The heat exchanger uses the residual heat of condensate water to heat water supply, which keeps the high-speed operation of the reboiler.
The jet condensers wash steam to remove the fibers and use dirty condensate water to produce hot water. It flash apart of dirty steam in the continuous operation, and the heat of steam is transferred to the white water.