JPS5831961B2 - Concentrator switching operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching operation method for a paper valve plant black liquor concentrator.

As used herein, "steam" refers to the steam generated in the concentrator, and "steam" refers to live steam for heating.

Switch operation means that when there are two types of liquid reservoirs, M, and two types of work equipment, R and S, at a certain point L is connected to R, M is connected to S, and at another point, L is connected to S, and vice versa. Refers to the operation of switching M to R and repeating this process.

The switching operation that affects the concentrator will be explained later.

Conventionally, vacuum evaporation multiple effect cans have long been used as black liquor concentrators in paper valve plants, for example.
The traditional method uses this vacuum evaporator to reduce the concentration of black liquor to 50-55.
%(TS)t, and this black liquor is further heated to 62 to 65
% (TS)t, and burned in a recovery boiler to recover chemicals.

Recently, however, the bad odor generated by direct contact type evaporators has become a problem from the standpoint of pollution prevention, and there has been a trend toward concentrating in vacuum evaporators to the desired final concentration of around 65%1.

The problem in this case is the scaling of the evaporator to high concentrations.

This often requires shutdown and appeal of the evaporator.

A forced circulation type evaporator, which is most resistant to scaling, is usually used as a concentrate for high-concentration black liquor, but even in this case, the continuous operation time of the final concentration concentrate is very short.

For this reason, it is most common to use 2 final concentration concentrates.
The method is to set up cans, one of which is a complete spare can, operate these two cans alternately, and conduct the appeal while the other can is resting.

However, in this case, a spare can is kept that does not contribute at all to normal operation, which increases equipment costs.

The scale components of black liquor are a mixture of inorganic substances such as mirabilite and calcium compounds, and organic substances such as grains. requires an appeal using a medicinal solution,
In extreme cases, mechanical cleaning using high-pressure water or the like may be required.

On the other hand, if scale adhesion is in its early stages, warm water can be used, and even if black liquor is used, dilute black liquor or low-concentration liquid can be used to prevent scaling rather than causing scale formation. It has been proven that it can be effective.

Therefore, in recent vacuum multiple effect evaporators for high concentration concentration, two final concentration concentration cans are installed, but one can is not used as a spare, but one of the final concentration cans is filled with dilute black liquor or low concentration black liquor. Since the liquid passes through and does not evaporate, it has an anti-inflammatory effect.

By alternating the cans through which this low-concentration black liquor is passed at regular intervals, continuous operation can be continued for long periods of time without causing scaling problems, so the evaporator used for appeals can be used as a process line rather than as a spare can. Can be included in equipment capacity.

This method of operating the final concentration canner alternately with high concentration liquid and low concentration liquid is called a switching operation method in which the concentrator is pressed.

As shown in Fig. 1, the conventional switching operation method is to install two identical evaporators, one evaporator and one 1B, and supply heating steam to these two cans in parallel, and the same amount of steam to a flow rate recording controller (FR).
C).

On the other hand, as for black liquor, which is the target liquid, for example, a medium concentration black liquor is supplied to the evaporator 1A, and a low concentration black liquor is supplied to the evaporator 1B.

At this time, the amount of liquid supplied to each can is also approximately the same.

In this case, the evaporator 1B serves as the final evaporator for high-concentration concentration, and the evaporator 1B performs the appeal operation without evaporating.

After running this for a certain period of time, scale will adhere to the final concentration can.
When the overall heat transfer coefficient of the can decreases by a specified value, the medium concentration liquid is supplied to the evaporator 1B and the low concentration liquid is supplied to the evaporator 1 by switching the valve, and the evaporator 1A is appealed.

2 is a heated steam supply pipe, 3 is a steam pipe that sends steam to the next can, 4 is a low concentration liquid pipe, 5 is a high concentration liquid pipe, 6 is a product outlet for taking out the product, 7 is a low concentration liquid outlet, 8 is the steam outlet.

As for control equipment, FRC is a flow rate recording controller, FIC is a flow rate indicating controller, LC is a level controller, and DRA is a density recording alarm.

This method has the following drawbacks.

(1) The amount of heating steam supplied to the evaporators IA and IB is kept constant.

Generally, the amount of heat input into the evaporator is determined by the following formula.

Q=UA△T Here, Q: Amount of heat input into the evaporator (if the heat source is steam, it is the product of the amount of steam and enthalpy) U: Overall heat transfer coefficient of the evaporator A: Transfer at the heated part of the evaporator Thermal area ΔT: Temperature difference between the steam and the liquid to be heated in the hot section of the evaporator As mentioned above, in this system, the evaporator IA.

Since the amount of steam supplied to evaporator 1B is constant, the value of Q can be considered to be the same for evaporators IA and IB.

The overall heat transfer coefficient U of the evaporator is greatly influenced by the concentration and temperature of the liquid to be heated.

Now, for example, if one evaporator is used as a final concentration concentrator and evaporator 1B is in operation, the U value of evaporator 1B will be more than twice that of one evaporator.

Since the heat transfer area A is shared between the evaporators IA and IB, ΔT inevitably changes, and the evaporator 1B has a smaller ΔT than that of one evaporator.

In other words, even though the evaporator has a capacity of 1, it is not used effectively.

(If the amount of steam can be changed, the amount of heat supplied can be increased by 1, where ΔT of the evaporator 1B is the same as that of one evaporator.

In other words, the amount of evaporation can be increased. ) (2) One evaporator and one person
When B is switched by switching a valve, for example, in the case of one evaporator, a low concentration liquid comes in while the evaporator is operating at the final concentration, so the concentration of the product taken out from the evaporator decreases. and the product will no longer be made into a product.

Further, as for the evaporator 1B, the medium concentration liquid is fed by switching, so the concentration gradually increases, but after a certain period of time, the product concentration is still not reached.

This state is shown by the solid line in Figure 5, and with this method of switching, 1 and 2 can be taken out as products.
It took ~3 hours and was extremely inefficient.

The present invention eliminates the above-mentioned drawbacks of the conventional method by changing the amount of steam input during switching operation according to the switching process, thereby effectively performing heat transfer in each evaporator and shortening the switching transition time. It is an object of the present invention to provide a switching operation method for a concentrator that can shorten the period of product instability after switching and increase operating efficiency.

In the present invention, a low concentration liquid to be treated and a medium concentration liquid to be treated are alternately flowed into two evaporators, and heated steam is supplied to each of the two evaporators, so that concentration and concentration are performed simultaneously. By pressing the button on the switching operation method of the concentrator, the flow rate of steam to each evaporator after switching is controlled by the program controller, and the overall heat transfer coefficient is determined by the appeal operation for the evaporator on the side where the intermediate concentration liquid to be treated flows into. Supply an amount of steam that takes into account the increase in the amount of steam, and supply the remaining steam to the evaporator on the side into which the low concentration liquid to be treated flows so that the sum of the steam flow rates to the two evaporators becomes a constant value. This is a switching operation method for a concentrator, characterized by the following.

The present invention will be described with reference to the drawings in accordance with an embodiment of the present invention. FIG. 2 shows a control operated by a program that changes the flow rate of steam injected into the evaporator 1 and 1B according to the progress of switching. The mechanism 9 provides a signal to the flow rate recording controller FRC to control it.

As mentioned before, evaporator IA. Among 1B cans, the overall heat transfer coefficient U of the cans that are being operated with low concentration liquid is larger than other cans, so by injecting the amount of steam commensurate with the increase in the U value, both evaporator cans Both IA and IB can effectively utilize the heat transfer area, increasing plant operating efficiency and reducing equipment costs.

If the amount of evaporation from evaporator cans 1 and 1B is output at full capacity according to the concentration of liquid in the cans, when the liquid supplied to evaporators 1 and 1B is changed by switching, it will be necessary to input steam for heating. The amount also needs to be changed.

At this time, if the amount of steam input is changed at the same time as the liquid supply is changed, the concentration of the liquid in the can will not change suddenly as described above, so if we look at the final concentration during concentration, the concentration will be 1.
However, an excessive amount of steam is injected until the temperature is lowered sufficiently, resulting in the disadvantage that the concentration temporarily increases too much and the switching time becomes longer.

Regarding the cans undergoing the appeal operation, the amount of steam decreases rapidly while the concentration inside the can is low, so it takes a long time to reach the final concentration.

Therefore, as shown in FIG. 3, the amount of steam fed into the high concentration can is increased over time, and the amount of steam fed into the low concentration can (appeal operated can) is decreased over time.

However, this drawback can be eliminated by program control so that the total amount of steam injected into both cans is always constant.

The amount of steam injected into each can is not only controlled linearly as shown in FIG.

As shown in FIG. 4, steam is introduced at the same rate as before the change for a certain period of time after the supply liquid is switched, and then both rates are reversed relatively quickly, thereby making the steam control more effective.

The state of change in the concentration of each can at this time is shown by the dotted line in FIG.

By controlling the amount of steam input to each can in this manner, the time required for the trench to complete switching and reach a new equilibrium state can be greatly shortened compared to the conventional switching method.

The above is a method of controlling the amount of steam input in order to maximize the capacity of the evaporator and shorten the switching time as much as possible, but for example, one person in the evaporator is concentrating the final concentration and evaporator 1B is operated as an appeal. It is assumed that switching is carried out as a medium and starts supplying a low concentration liquid to the evaporator 1A and a medium concentration liquid to the evaporator 1B.

At this time, the amount of heating steam is program-controlled as shown in the above example.

At the same time as controlling the amount of steam, the flow rate indicator FIC for low concentration liquid is connected to the control mechanism 9, and the amount of medium concentration liquid fed to 1B is controlled for a certain period of time from the start of switching according to the switching process, for example, during steady operation. Approximately 60-70
By narrowing down the concentration, it is possible to further increase the rate of increase in the concentration of the liquid in the evaporator 1B.

The present invention relates to switching operation of a concentrator.

By controlling the amount of steam injected into each evaporator of two evaporators to which target liquids of different concentrations are alternately supplied according to the switching process, the optimum conditions for heat transfer in each evaporator can be achieved. To provide a switching operation method for a concentrator, which can perform effective concentration by bringing the concentration close to each other, shorten the switching transition time, shorten the unstable period of the product after switching, and improve the operating efficiency. This has an extremely effective effect in practical terms.

[Brief explanation of the drawing]

Figure 1 is a flow sheet of an example of a conventional concentrator, Figure 2 is a flow sheet of an example of a concentrator using the method of the present invention, and Figures 3 and 4 are graphs showing the relationship between steam supply amount and time. ,
FIG. 5 is a graph showing the state of density change. IA, IB... Evaporator, 2... Heating steam supply pipe, 3... Steam pipe, 4... Low concentration liquid pipe, 5... Medium concentration liquid pipe, 6... Product outlet, 7...Low concentration liquid outlet,
Exit, 9...control mechanism. 8...Steam extractor

Claims (1)

[Claims] 1. A concentrating device in which a low concentration liquid to be treated and a medium concentration liquid to be treated are alternately introduced into two evaporators, heated steam is supplied to each of the two evaporators, and concentration and appeal are performed simultaneously. In the switching operation method,
After switching, the flow rate of steam to each evaporator is controlled by a program controller, and an amount of steam is supplied to the evaporator on the side into which the intermediate concentration liquid to be treated is in consideration of the increase in the overall heat transfer coefficient due to the appeal operation. , and a switching operation of the concentrator, characterized in that the remaining steam is supplied to the evaporator on the side into which the low concentration liquid to be treated flows so that the sum of the flow rates of steam to the two evaporators becomes a constant value. Method.