Method for the continuous steam pre-treatment of chips during the production of cellulose pulp
The arrangement and method are for the steam pre-treatment of chips during the production of cellulose pulp to avoid the blow-through of gases in the steam pre-treatment vessel. This prevents foul-smelling gases from being released into the atmosphere. Spreader nozzles for the injection of cooling fluid are arranged in the gas phase of the steam pre-treatment vessel. In the event of the risk for blow-through of steam, cooling that is proportional to the risk is activated. It is possible to avoid the emission of gases from the chip bin when interruptions in the process occur, whereby the release of odors into the surroundings can be minimized.
1. A method for a continuous steam pre-treatment of chips during a production of cellulose pulp, comprising:
feeding untreated chips, that are at a temperature that corresponds to an ambient temperature, to a steam pre-treatment vessel,
pre-treating the untreated chips with steam to pre-heat the chips and expel air that is contained in the chips, where the steam pre-treatment vessel has a chips inlet defined therein at a top and an outlet defined therein at a bottom,
adding steam (ST) to a bed of chips that has been established in the steam pre-treatment vessel through a steam generation device,
establishing a temperature gradient in the bed of chips,
establishing a high temperature low down in the bed of chips,
establishing a low temperature at an upper surface of the bed of chips, the low temperature being a temperature lower than the high temperature,
detecting an operational parameter that exceeds a threshold value indicating a blow-through of steam up through the bed of chips,
arranging a regulator valve in a connecting line between the source (CS) of cooling liquid and the pre-treatment vessel, and
the operational parameter exceeding the threshold value triggering an opening of the regulator valve through an activation device to permit a cooling liquid from a source (CS) to flow therethrough, and injecting the cooling liquid into the top of the pre-treatment vessel.
2. The method according to claim 1 , wherein the step of injecting is activated when a temperature in the upper surface of the bed of chips exceeds a threshold value.
3. The method according to claim 1 , wherein the step of injecting is activated when a flow of chips into or out from the steam pre-treatment vessel falls below a threshold value.
4. The method according to claim 1 wherein water or cooled process liquids from a production process for cellulose pulp is used as cooling liquid.
5. The method according to claim 4 , wherein an amount of cooling liquid that is injected is controlled to be proportional to the risk of blow-through.
6. The method according to claim 5 , wherein an amount of cooling liquid that is injected is controlled by activating different numbers of injection nozzles or by pulse width modulation.
7. The method according to claim 1 wherein a probe detects a value for the low temperature in the pre-treatment vessel and sends an output signal to a control unit to regulate the regulator valve.