FI61532C - FOERFARANDE FOER FOERBAETTRING AV EFTERANVAENDNINGEN AV VID TILVERKNINGSPROCESSEN FOER TRAESLIPMASSA ALSTRAD VAERMEENER GI - Google Patents

Description

61532

The present invention relates to a method for improving the recovery of thermal energy generated in the production process where there is an absolute pressure of more than one atmosphere, - hot jet water is sprayed into the grinding chamber, - the pulp pulp is passed from the grinding chamber to a steam separator replacement water to compensate for jet water losses, 20 - the steam released from the steam separator is recovered for the subsequent use of the thermal energy contained therein, and - the pulp pulp leaving the precipitator is taken to recover the thermal energy it contains for after-use.

Pre-pressurized grinding is known (F1-pa-25 exam applications 782414, 780514 and 780515, SE patent application 7411949-6, SE patents 318178 and 336952), in which grinding takes place in a grinding room under pressure at more than one atmosphere. The supply of wood to the overpressure sanding space takes place, for example, by means of 30 pressure equalization chambers built on top of the sanding pockets of the sanding machine. The grinding space delimited by the shutters and the mass basin is preferably pressurized by means of air or compressed steam. The wood is defibered by pressing the wooden dust against the grindstone with the help of a hydraulic piston. The vibration and frictional heat generated by the grinding bed, together with the spray water sprayed on the surface of the grinding bed, detaches the fibers from the wood.

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The temperature of the spray water has been found to play a greater role in fiberization in pressurized grinding than in non-pressurized grinding. The warmer the shower streams, the longer and more complete the loose fibers 5 of the wood material and the stronger the paper made from these fibers. It is therefore advantageous for pressurized grinding the warmer the jet water is returned to the grinder.

After defibering, the pulp pulp is discharged from the grinding pad 10 by means of a tube in which, before adjusting the amount of pulp flow, the sticks and larger pieces of wood in the pulp pulp are comminuted by a stick crusher. The temperature of the pulp discharged from the grinding chamber is normally above 100 ° C. Depending on the temperature of the spray water and the overpressure of the grinding chamber, the temperature of the pulp may rise up to 145 ° C under practical conditions. In this case, the inlet temperature of the spray water to the grinding chamber must be 130-135 ° C and the overpressure of the grinding chamber 3 bar. The thermal energy bound to the pulp stock is released in the form of steam in a steam separator, where the pressure is reduced to 20 atmospheric pressures, since the temperature of the pulp after the steam separator must be below the boiling point of water. From the steam separator, the pulp can be led directly to a precipitator, where the hot jet water is separated from the pulp for return to the grinding chamber. From the steam separator, the pulp can also be discharged into an intermediate tank 25, from where it is passed to various sortings: pressure sorting and vortex cleaning before being passed to a precipitator where the hot shower water is separated from the pulp. The pulp is removed from the precipitate at a consistency of 5-33%.

With the pulp leaving the precipitator, 2-20% of hot spray water leaves the system. This amount and any other losses must be replaced by replacement water entering the system and entering the post-precipitator spray water tank. In known systems, the amount of additional water introduced into the system over a longer period of time corresponds to the amount of water leaving the pulp stock 35, and the temperature of the additional water introduced into the system is kept as high as possible to keep the temperature of the jet water entering the grinding space as low as possible.

The electrical energy fed to the grinder is almost 100% converted in the grinder-5 machine into thermal energy bound to the pulp and the jet water. When the grinder is operating in equilibrium, ie when the temperatures of the various points of the grinder are constant, as much energy is removed from the grinder as is brought into it. There are basically three paths to energy: 10 1. With the steam released in the steam separator 2. With the pulp stock for the paper machine 3. As a loss through the milling and through the walls to the environment.

15 The amount of losses depends mainly on the structure of the plant and the difference between the process temperature and the ambient temperature.

The energy / unit of time taken by the pulp stock can be calculated from the following equation: 20 p cp · "(tl - S» where P = displaced power (kW) 25 Cp = specific heat of the pulp stock (kJ / kg ° C) m = pulp stock flow rate (kg / s) tfc = average temperature of the incoming make-up water (° C) t ^ = average temperature of the outgoing pulp stock (° C) 30 The remaining energy is released as steam in the steam separator.

A disadvantage of the previously known system is that the distribution of thermal energy generated in the grinding process with either steam or pulp cannot be influenced.

35 There are often driving situations that would be advantageous to get '/ • jj ·; ·.

61532 4 more energy than normal from grinding with the pulp to a paper machine, to which the pulp continues its journey after various steps. On the other hand, often the water and pulp systems of a paper mill are constantly in an unstable state and the temperature of the pulp coming to the paper machine 5 varies for several different reasons. However, a stable temperature would be advantageous for the operation of the paper machine. The constant energy flow / pulp weight unit fed from the grinder does not aim to compensate for this variation.

10 In winter, the released steam may have a very profitable use, while in summer the steam may be wasted. Lowering and raising the temperature level of the paper machine's stern according to the seasons could have a significant effect on the mill's energy economy without compromising production or product quality. This is not possible with the current known system.

The object of the present invention is to provide a method which eliminates the above-mentioned drawbacks and provides better possibilities for the economical selection of the heat energy consumption objects generated in the production process of the wood chips 20 based on pressure grinding when conditions change. This object is achieved by the method according to the invention, which is characterized in that additional water is introduced into the pulp pulp to control the energy distribution between the thermal energy contained in the steam released from the steam separator and the thermal energy contained in the pulp pulp leaving the steam separator.

The invention is based on the idea that by changing the temperature of the pulp stock from the grinding chamber, either by the amount of additional water introduced into the system and / or the temperature, the distribution of heat energy generated in the process can be influenced.

The invention will be explained in more detail below with reference to the accompanying drawing, which schematically shows a pressure grinding process operating according to the invention.

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The drawing shows a grinding machine 1 with a rotating grinding stone 2 mounted on a pressurized grinding chamber 3. The grinding chamber is associated with two grinding pockets 4, above which are arranged equal pressure chambers 5 closed by shutters. to press against the grindstone.

A number of spray pipes 7 are arranged in the grinding space for conducting warm spray water to the surface of the grinding stone. In order to collect the grinding mass 10, a mass basin 8 is arranged in the grinding space.

From the pulp basin of the grinder, a pipe 9 for the pulp stock A leads through a stick crusher 10 and a butt valve 10a to a steam separator 11 provided with a steam removal pipe 12 for the steam H released from the pulp stock.

From the steam separator, a pipe 13 leads to the steam pulp B released from the steam to the intermediate tank 14. From the intermediate tank, a pipe 15 leads through the pump 16 and the pressure sorter 17 to the precipitator 18 for the pulp pulp C to be precipitated. The precipitator is provided with an outlet 19 for the doped pulp D 20.

The precipitator has a basin 20 for water F leaving the pulp stock C to be precipitated. From the basin, a pipe 21 leads to an intermediate tank 22. From the intermediate tank, a pipe 23 leads through a pump 24 to jet pipes 7 in the grinding space for conducting warm jet water 25 to said jet pipes.

When preparing wood chips, the shower water continuously circulates through a circulation system formed by pipes 9-13-15-21-23. Some of the jet water leaves with the precipitated ground pulp and due to other water losses in the process, escaping steam, etc., more additional water has to be added to the circulation system than what is left from the precipitator alone with the pulp.

The additional water E is introduced into the pipe 9 after the stick crusher 10 before the steam separator 11 by the pipe 25. The amount of additional water 35 is controlled by a valve 26 controlled by controllers 27. The controller can receive its control command 28 e.g. from paper machine head or the temperature or pressure at the point of consumption of the steam released from one of the steam separators.

5 In order to ensure the height of the lower surface of the tank 22, additional water is also supplied to the system via the valve 29. The position of the valve is controlled by the controller 30 according to the command received from the level transmitter 31.

The heated excess water J introduced into the process is pumped by 10 pumps 32 along the piping 33 to the later stages of the papermaking process as dilution and replacement water.

The previously known system works as follows:

The temperature of the pulp pulp from the grinder 1 should be 9 115 ° C in the pipe 15 and the flow rate 80 kg / s. The amount of additional water E introduced in the pipe 25 should be 10 kg / s and the temperature 50 ° C. The temperature of the pulp stock A before the steam separator is then 80. 115 ° C + 10 · 50 ° C =? gOc 20 (80 + 10) In the steam separator, the pulp stock cools to 100 ° C and releases 1.30 kg / s of steam. The heat output transferred with the steam is then 2.9 MW. If more energy were now desired for the paper machine 25 to raise the headbox temperature, it would not be possible in the known system without structural changes.

The system based on the method according to the invention operates as follows: The controller 27 receives its control command 28 and the valve 26 opens and the amount of additional water E increases. Let the opening be so large at first that the water flow E doubles. The temperature of the stock A coming before the steam separator is then 35 80 · 115 ° C + 20 - 50 ° C = 102oc 80 + 20 7 61532

The amount of steam released then decreases to 0.37 kg / s and the heat output with the steam is only 0.84 MW. The operation of the controller can be controlled either so that the change in the position of the valve is directly proportional to the difference between the measured value and the setpoint, or the entire control system operates according to the logic programmed into the computer.

An additional 20 kg / s of water is now introduced into the process, although only 10 kg / s can be allowed to leave the precipitator with the pulp to maintain the desired level of consistency. The imported excess water J is collected by a precipitator 18 in a basin 22, from where it is pumped by a pump 32 along a pipeline 33, e.g. as dilution water to the later stages of the papermaking process.

The same result can be obtained by lowering the temperature tfc of the additional water E in the above equation.

Alternatively, it may be possible to reduce the amount of energy going to the paper machine, e.g. In the known system, this is also not possible.

In the method according to the invention, this can be achieved by reducing the amount of incoming additional water E. If the amount of additional water-25 E corresponds to the amount of water going from the precipitator with the pulp stock D and other losses, the amount of additional water can no longer be reduced. It can be seen from the equation that only the reduction of the temperature difference (t ^ - tfc) is possible.

In the exemplary process 30, it is possible to reduce the temperature difference by raising the temperature tt of the incoming additional water E. If, as an additional water, + 50 ° C can be used as additional water, eg max + 60 ° C, the temperature of the water entering the steam separator is 35 80, - 115 ° C 4- 10 - 60 ° C = 1Q8 / 9oc> 90 S "* - · V · '61532 8

The amount of steam released is 1.48 kg / s and the heat output transferred with the steam is then 3.3 MW.

Thus, in this exemplary case, the method according to the invention makes it possible to control the amount of steam released in the cyclone between 0.37 and 1.48 kg / s and the heat output with it, respectively, from 0.84 MW to 3.3 MW.

The drawing and the related method are only intended to illustrate the idea of the invention. The details of the method according to the invention can vary considerably within the scope of the claims. The additional water E introduced into the system can be led to a point in the jet water circulation 9-13-15-21-23 other than before the steam separator 11, for example between the steam separator 11 and the precipitator 18, the precipitator 18, the intermediate tank 22 or the spray water pipe 23.

In this case, the additional water enters the pulp stock A and affects the energy distribution in the steam generator 11 only in the next cycle, i.e. after the additional water has passed through the grinding space 3.

Claims (6)

1. A method for improving the post-use of thermal energy generated during the wood grinding process manufacturing process, according to which the process - wood is ground with a rotary grinding means (2) in a grinding room (3), whereby an absolute pressure exceeding one atmosphere rises, - in the grinding room is injected hot. water (G), 10. the mass (A) is transferred from the grinding room to a meadow separator (11), whereby the heat-bound thermal energy is released as a meadow (H), - the mass is transferred from the meadow separator to a precipitation device (18), released water is returned to the grinding room as spray water; (D) is recovered to utilize the thermal energy contained therein, characterized in that additional water (E) is added to the mass (A) gating the energy distribution between one side of the heat energy contained in the meadow released from the meadow separator (H) and on the other hand the heat energy contained in the mass leaving the meadow separator (B). 2. A method according to claim 1, characterized in that the amount of additional water (E) introduced into the pulp (A) is controlled. Method according to claim 1 or 2, characterized in that the temperature of the additional water (E) introduced to the mass (A) is controlled. 35 4. A process according to claim 2 or 3, characterized in that the amount of additional water. I - +