SE464637B - SET TO REGULATE THE TREATMENT TEMPERATURE IN A GRINDING - Google Patents

Description

464 637 10 15 20 25 30 35 drains as regularly as possible, and that the manufactured slip the quality of the pulp is maintained at a high, constant level.

This task is solved in the manner specified in the characterizing part of claim 1.

The inventors have noted the following: The instability (which in a known way is expressed through a variation tion of the specific power requirement) is always followed by variations of trough temperature. Attempts have subsequently confirmed that of the trough temperature has a decisive influence on instability, and thus also on the quality of the abrasive mass. It will be appreciated that trough temperature the tour varies due to all possible magnitudes. Through con- stance keeping within very small limits also keeps the quality high and constant level.

As mentioned at the outset, it was already known that the temperature above a certain minimum value ("hot mass".

It was also known that crucial for a sharp increase in trough the stock temperature is, among other things, a too low wood feed or a poor, such as wear, stone surface and that such an increase may act in a similar way by increasing the wood feed, which of course generally also be linked to a corresponding increase in splash water quantity, often also by lowering the stock level or increasing the the density of the stock and finally by taking the grinder out of operation to be able to sharpen the stone.

Thus, it was not aware that a direct impact on the inertia the temperature could stabilize the conditions in the grinding zone and this moreover, especially when the trough temperature is already at an upper limit.

Of course, additional measures can also be put in place, such as with hot water to clean the stone, to in principle improve the sanding process or the quality of the sanding compound. Of course must even the grinding intervals of the stone are kept. 10 15 20 25 30 35 464 637 In the following, the device according to the invention will be described in a preferred embodiment with reference to a control diagram, which is shown in Fig. 1a. In Fig. 1b the corresponding function is shown. diagram for the control components and in Fig. 2 is shown in principle a grinding mill with its control device.

Fig. 2 shows in principle a magazine grinder, in which the round wood is supplied via a conveyor belt 31 to the feed shaft, which side led by the food chains 30.

The feed chains 30 press the round wood against the grindstone 2, which during splashing water spray processes this into abrasive mass suspension which collected in the grinding tray. Level of abrasive mass suspension in the abrasive trough 8 is regulated by means of a pressure sensor 11 via a regulator 22, which via a actuator motor 12 controls a valve 10 in the drain trough drain line 9. For disassembly of trays is located in front of the outlet line 9 mounted one chip chewing 24 whose rotating knives cooperate with fixed knives 23. Via line 3 is fed to the grinding trough with dilution water, which is sprayed out by means of nozzles 7. The temperature of the dilution water, which is usually is hot return water from the factory plant, can be cold water via line 4, is set by means of the The temperature in the grinding trough is then applied the control device 1 via the sensor 6. By means of the controller 1, the temperature is thus maintained. the temperature of this abrasive mass suspension in the abrasive trough is substantially constant, for example at about 85 ° C. It has turned out to be quite high temperature of the abrasive mass suspension in the abrasive tray (trough temperature turn) is very advantageous for a good grinding process. You could say that the higher the temperature in the grinding trough, the higher the temperature the trip in the grinding zone at the grindstone. Correspondingly, it also improves the quality of the abrasive. However, the temperature must not be selected resp rise so high that it causes an increased evaporation in the grinding zone, which then as is well known, where predominantly arises patially. By violently tearing fibers from the wood joint causes the stone in this case fiber pieces or short fibers while striving to get through smoothly grinding to produce an abrasive pulp suspension with relatively long fibers.

At this grinding plant of open construction, at which the operation thus 464 637 10 15 20 25 30 35 can only occur at atmospheric pressure, however, the temperature gets below under no circumstances exceed the limit range 90 ° C to approximately 95 ° C.

With the help of the temperature sensor 6 and the temperature controller 1, you can see now that the temperature in the grinding trough does not rise unauthorized much.

Namely, it has been shown that the irregularities in the grinding process makes itself noticeable through a rising trough temperature. By careful measurement of the trough temperature can thus be prevented very quickly respectively remedy these irregularities, thereby lowering the trough temperature thus kept in the range of approximately AK to 8K below the limit of eg 92 ° C. Despite this described measure, there are now operating conditions, during which it is not readily possible to maintain the trough temperature constant. Such operating conditions arise especially when, for example, wood humidity varies greatly and suddenly very dry wood must be ground. It is just as risky when the round wood in the tie shaft comes obliquely or that the round wood is even substantially sanded on the end surfaces. The specific work effect of the grinding plant then increases very sharply to impermissibly high values at which the quality of the abrasive mass decreases very powerful. On such occasions, one often has to, if not take action taken at the right time, reduce the grinding effect very sharply, and this moreover, for a fairly long time, which of course intrudes very strong on production capacity.Of course related these operating conditions even with an increase in the grinding trough temperature.

However, the described regulation for constant holding is in itself himself often resp usually not enough. On such occasions therefore uses the regulatory procedure that will be described in it the following with reference to Figures 1a and 1b. For this purpose the specific work effect is measured. This is obtained as the ratio between engine power and the amount of ground wood, preferably measured as number of 100 kg at per hour. Then the limit value for the specific coffee work range from about 120 to 130, if the engine electric load is measured in kilowatts. The amount of ground wood can be determined in this case. by measuring the feed of the grinding chains 30. The signals corresponding to the specific working power is processed in a low-pass file. so as to obtain diagram B, in which the specific working the effect is displayed as a function of time. From this curve is formed by a limit sensor 13 with differential input a sequence of pulses, 10 15 20 25 30 35 464 637 which are added to an integrator 14 which may be included in an electronic counter. In this, an upward constant is calculated upwards, or with a frequency proportional to the magnitude of the exceedance below the time periods exceeding the limit value exist and down by one about four to five times Lower frequency during the other time periods as shown in diagram D. For example, the limit value in the integrator is reached 14 at time t1, this gives an impulse to magnitude integration This then preferably gives, for example via digital-to-analog conversion Laren 16, an error signal of eg constant 5 ° C as a magnitude of the regulator 1. Of course, a corresponding degree could also be reduced the setpoint of the trough temperature. An analogous structure of this stability regulation is of course also possible, but should time may be more difficult to achieve in the case of corresponding claims on the proximity of the same. The magnitude is then reduced to zero in uniform steps for a fixed period of time of, for example, 10 or 20 minutes. unless there is a further disturbance from the integrator 14, which is the case when the integrator 14 in the meantime again corresponding counter position has been achieved as a result of the corresponding long limit exceeding the specific work effect which is the case in diagram D at time t2.

In this case, the size was already almost completely reduced. IN in each case, however, the magnitude of up to the maximum is switched the value of the error signal of eg constant 5 ° into the controller. This magnitude is suitably fed into the actual input of the controller 1.

This simulates an excessively high temperature in the grinding trough, so that it via the valve 5 tries to respond to this by means of cold water supply temperature rise. With a corresponding lowering of the grinding trough temperature can in most cases be achieved, that the unwanted operating condition quickly overcome. Production disruptions are thereby largely prevented to perform for a long time.

In this mode of operation, the electricity absorbed by the grindstone drive motor too high a load, the wood feed is reduced in corresponding degree so that in any case impermissible operating conditions vikes. The pulp quality produced is also very good and almost corresponds to that of the so-called pressure grinder, at which 464 637 10 15 20 25 39 35 the wood is ground in a closed grinding house at a pressure of approximately 1.5 bar below correspondingly high temperature effect of eg 115 ° C. In any case, the device according to the invention is a much simpler and cheaper construction of the grinding plant in relation to the pressure grinding the work.

In the event that the immersion depth of the grindstone in the trough is too high Small, you can also arrange it so that you do not affect the temperature of the dilution water for the trachea, ie cools this, without instead, for example, regulates the temperature of the shaft water that is located in the shaft intended for round wood 26.

If there is no such shaft water, it can also be regulated, ie in this case reduce, the temperature of the splash water, which by means of nozzles 25 spray directly on the grindstone. This is best done via a heat exchanger or alternatively by mixing cold water in the standing water.

The regulation of the shaft water temperature could also be taken as a supplement to the regulation of the trough temperature Instead of regulating the temperature of the trough or shaft water, it could in principle be beneficial to under only use the previously described regulation of temperature the temperature of the splash water, which within a certain surface area of the grinding the stone is sprayed on it before it enters the grinding zone itself.

In this case as well as in the other cases, inertia could be measured. the temperature of the stock and this preferably by measuring at several measuring points determine an average value. To determine one such an average value is also possible in cases where the temperature measurement performed by means of several temperature sensors 6 on the abrasive mass pension that sprays out on the outlet side of the grindstone. On the other hand is the measurement of the shaft water temperature is not suitable, as it is not possible to place measuring sensors between the round wood.

In the event that the temperature is measured on the abrasive mass that sprays out of the grindstone, one can further raise the above-mentioned limit the value of the temperature. You can even go as an upper limit 10 15 20 464 657 up to 10000 as the measured temperature of the spraying mass the suspension. This is especially true when you have a sufficiently high level of shaft water above the grinding zone, which slightly increases the boiling point.

If one can imagine an even larger range of devices for measuring irregularities in the grinding plant's specific working effect, so you can in principle do not set a limit value for it and detect any change that is, especially the increases of the specific work effect.

You can then evaluate the different slopes to a corresponding degree differently strongly, for example on a counter expect higher frequency at stronger inclination. At a certain limit value for the position of the counter is generated then as in the method described above, the error signal or correction the signal for lowering the setpoint temperature of the trough stock, the shaft water or the splash water. Otherwise, the process is exactly like that shown in Diagrams D and E in Figure 1b.

However, it has been shown that it first described the procedure to fully corresponds to the requirements and that the operation of the grinding plant is thereby mastered. p

Claims (1)

464 637 10 15 20 25 30 8 Patent claim A method of regulating the trough temperature in a grinding plant at which round wood is ground to an abrasive mass suspension, especially at atmospheric pressure, if applicable during water spraying in a reservoir or shaft (26) by means of a grindstone (2), which preferably dips into the trough, k characterized in that the trough temperature and / or the water temperature in the shaft (26) is kept below an upper limit value, whereby the trough temperature is affected by varying the temperature of the trough dilution water or grinding splash water and that a signal is given to reduce the trough temperature or trough temperature. longer duration and more frequent exceeding of a limit value for the grinding plant's specific working power, taking into account the time intervals between the occasions that occur, during which the grinding plant's limit value for the specific working effect is below. A method according to claim 1, characterized in that the time intervals for not exceeding the specific working power of the grinding mill are taken into account to a proportionally lesser extent than the time periods during which the limit value for the specific working power is exceeded. A method according to claim 2, characterized in that depending on a certain limit value of the total sum of the periods during which the limit value for the specific working power of the grinding mill is exceeded, a signal for reduction of slurry temperature is generated with regard to the corresponding interval of non-exceeding the trip, the shaft water temperature or the standing water temperature. A method according to claim 3, characterized in that the signal, until a new corresponding signal for temperature reduction occurs, starting shortly after it is delivered, is reduced uniformly or in uniform steps towards zero. Method according to claim 1, characterized in that sharp decreases in the specific working power of the grinding mill, corresponding to the slope of the respective increase in the specific working power, are detected with a corresponding estimate of this slope and that the estimates of the slopes are summed up to a limit value, from which a new detection of the slopes takes place and a signal is issued either to reduce the trough temperature, the shaft water temperature or the standing water temperature or a corresponding upward correction of the actual value of the corresponding temperature is performed, this signal, starting shortly after it is given, eats are reduced uniformly or in uniform steps towards zero.