JPH0152657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for combusting liquids in a recovery boiler by varying the chemical and physical consistency of the liquid to obtain a suitable droplet size for combustion within the recovery boiler. The present invention relates to a method for regulating the supply of liquid to a recovery boiler.
The invention also relates to the use of the above method for regulating combustion in a continuously operating recovery boiler for burning dissimilar wood and/or liquids such as effluents from sulfate and sulfite boilers. It is.

As is well known, when chemical pulp is evaporated, waste liquid is produced, and the process of chemical pulp manufacturing is to recover as completely as possible the thermal contents and chemicals in this waste liquid and utilize them in the chemical pulp manufacturing process. This is particularly important from the economic standpoint. Prior to combusting the effluent to release thermal energy and recover chemicals, water is evaporated from the effluent to yield a combustion liquid containing about 40% water. By burning this combustion liquid in a recovery boiler, the thermal energy released can be used in the chemical pulping process, and the chemicals can be recovered from the bottom of the recovery boiler and used for the production of cooking liquor after regeneration. .

As energy prices continue to rise, having this liquid combustion function as a stable and efficient energy source in a recovery boiler is important from an economic standpoint in the chemical pulp manufacturing process.

The recovery and regeneration of salts for the cooking liquor, which is the main role of the recovery boiler, is performed at the bottom of the recovery boiler, which has a high-temperature reduction section with a so-called stack. The degree of regeneration in the boiler is measured by the reduction of sulfur. Salt recovery is measured by chemical loss. This loss occurs when it is emitted with the flue gas, for example as SO ₂ gas.

Another role of the recovery boiler is to recover heat from the flue gas. Heat recovery efficiency can be measured by the amount of flue gas loss, the proportion of non-flammable gases, and by the availability of the boiler, i.e. the laying days due to contamination of the flame surface.

A number of different parameters affect recovery boiler functionality. Another parameter is the relatively high amount of moisture (approximately 40%) in the combustion liquid fed to the recovery boiler. This amount of water is evaporated in the recovery boiler, but substantial evaporation occurs before the droplets falling toward the stack at the bottom of the recovery boiler reach the stack surface. If it does not evaporate before reaching the stack surface, most of the water will evaporate from the stack surface and the temperature of the stack will decrease, thereby increasing the release of sulfur dioxide. If the water evaporates before reaching the stack, the droplets become lighter and are carried along with the rising gas flow in the recovery boiler where they pyrolyze and burn in the gas phase, increasing the dust load of the gas. Therefore, the droplet size is adjusted so that when the droplet touches the stack surface, the dry solids content is adequate and the small amount of water that remains quickly evaporates from the stack surface, resulting in a porous stack. It is necessary to adjust the If you do this,
The stack at the bottom of the boiler becomes hot, which reduces SO ₂ emissions and improves boiler efficiency.

From the point of view of the functionality of the recovery boiler, the preferred droplet size is determined visually and empirically.
In particular, it is determined by checking the stack temperature at the bottom of the recovery boiler based on color. It has been established that the viscosity of the liquid supplied to the recovery boiler primarily determines the droplet size, especially if the size and type of nozzle supplying the liquid to the recovery boiler and the supply pressure remain essentially unchanged. . Similarly, if the liquid viscosity and flow rate remain unchanged, the nozzle diameter determines the droplet size.

In order to maintain the droplet size at a value that shows experimentally good results in the manner described above, the density or dry solids content of the combustion liquid, as measured by a refractometer, is used as a control variable. Based on the measurements, modifications to be made to the temperature and atomization pressure of the liquid fed to the recovery boiler were determined to obtain the desired size liquid droplet for the gas space of the recovery boiler. Primarily, the viscosity of the liquid is adjusted by heating the liquid. This type of adjustment is discussed in Pulp and Paper, 53;
(1979), 9, pp. 142-145.

Baume measurement is generally used to measure density. Refractometer measurements give quantities that can be used to control the recovery boiler if the feedstock and cellulose cooking conditions remain unchanged.

Disturbance-free operation of recovery boilers has long been achieved by keeping the method of production of the combustion liquid and the resulting properties of the combustion liquid as uniform as possible. This allows the combustion process to proceed with constant regulation. Conventionally, 1
In one mill, only one wood quality defined by that mill was generally used, and one particular pulp was generally produced as well. Therefore, the chemical consistency of the waste liquid generally remained unchanged. Instead, the dry solids content of the combustion liquid follows the function of the evaporation plant, with dynamic limits generally ranging from 55 to 60% dry solids.

The functioning of the evaporation plant was adjusted to obtain a certain dry solids consistency and the combustion process was adjusted according to this value. The dry solids consistency was adjusted to an accuracy of approximately ±1.5%. This large variation affects the use of recovery boilers by changing the degree of reduction, SO ₂ gas emissions and boiler pollution. When a problem arises, the user of the recovery boiler requests that the process values in the evaporation or steaming plants be checked to see if they are within set limits.

Continuous operation boilers were developed to increase the efficiency of pulp mills. In these boilers, various conditions change rapidly, for example if the quality of the wood used as raw material changes once in a while, or if the yield of steaming changes. A closed process, ie, a closed chemical cycle, also results in variations in the chemical consistency of the combustion liquid. These raw material variations also require new cooking values (residual alkali content) which further deteriorate the functionality of the evaporation plant. Under these conditions, it is not possible to maintain the properties of the liquid to be the same quality as before. For example, the second
The figure shows the relationship between the dry solids content and viscosity of the steaming waste from birch wood (area A) and the steamer's waste liquid from pine wood (area B). Even if the liquid has a certain amount of water, its viscosity will vary depending on the quality of the wood.

In the case of continuous steaming, the disturbances will be directly applied to the recovery boiler unless special measures are taken to store the liquid.

To achieve even better thermal energy economy, the dry solids consistency of the liquid is increased from a conventional level of about 60% to a level of about 76%. To ensure the same environment in the furnace due to atomization, the precision requirements during evaporation are greater with 67% liquid than with 60% liquid. According to Fig. 1, Fig. 1 is a graph showing the relationship between changes in dry solid content and viscosity of the same liquid sample.As can be seen from this graph, in order to maintain the same viscosity fluctuation range, ± ±0.4% variation in dry solids of 1.5%
must be reduced to

In addition to the above-mentioned large disturbances appearing in the recovery boiler, the demands placed on the operating results of the equipment,
Demands have also increased, for example on SO ₂ and H ₂ S levels in the flue gas.

In addition to the problems mentioned above, such as the increased demands placed on the operating results of recovery boilers and the relatively high losses from the recovery boiler of sulfur, which must be recovered as cooking salts, problems such as wood quality and If the cooking conditions are changed during pulp cooking such that the chemical consistency of the combustion liquid fed to the recovery boiler varies;
It has been demonstrated that conventional dry solids measurement methods, such as those described above, do not provide any reliable information about the size of the droplets formed within the gas space of a recovery boiler. Furthermore, the dry solids content is 65%
Above this point, the combustion liquid density measurements taken at Baume proved unreliable. Moreover, the time delay for dry solids analysis is quite large (approximately 12 hours), making it difficult to perform an analysis that is compatible with rapid changes in the chemical consistency of the combustion liquid fed to the recovery boiler. cannot be used for recovery boiler control.

It is therefore an object of the present invention to maintain the feed parameters of the combustion liquid fed to the recovery boiler at desired values that have been experimentally found to be good, or within set limits, so as to be as possible from a combustion point of view. It is an object of the present invention to provide a method in which a suitable liquid droplet is formed in a recovery boiler. The method according to the invention is particularly applicable when the chemical consistency and physical properties of the liquid fed to the recovery boiler change. This variation can occur, for example, due to the fact that the combustion liquid comes from a pulp cooking process (FIG. 2), where different wood qualities are used as raw materials, or from completely different types of cooking processes. Therefore, the method of the present invention involves combustion in a recovery boiler in which different types of cooking waste liquids obtained when different types of wood are steamed or different types of cooking waste liquids obtained when different types of cooking chemicals are used for cooking are combusted. Particularly suitable for adjusting.

According to the invention, the viscosity of the combustion liquid supplied to the recovery boiler is measured at least immediately before supply;
This measurement is used as a control variable to adjust the supply pressure, viscosity, and/or opening of the combustion liquid supply nozzle of the liquid supplied to the recovery boiler to obtain the appropriate droplet size. For example, the viscosity can be measured at a large number of locations for preliminary coarse control.

Using directly the physical properties of the combustion liquid that most affect the liquid dosing type as control variables, variations in the chemical consistency and physical properties of the liquid do not disturb the uniformity of the combustion process in the recovery boiler.

In a preferred embodiment of the invention, the combustion liquid fed to the recovery boiler is cooled or heated to adjust its viscosity. In contrast to previously known methods, cooling or heating is applied directly on the basis of viscosity measurements, without using the dry solids content of the liquid or refraction measurements as control variables. The viscosity of the combustion liquid is based on measurements maintained between two limiting values that have been experimentally found to be good. The cooling and heating of the combustion liquid is based on the rate at which its viscosity decreases to the lowest value of the limiting value or increases to the highest value, i.e., the gradient of the viscosity.
Can be effectively controlled.

Alternatively, the viscosity of the combustion liquid can be adjusted by mixing liquids with different viscosities into the combustion liquid. In this way, the method according to the invention burns different types of cooking waste liquors obtained when different types of wood are steamed or different types of cooking waste liquors obtained when different types of cooking chemicals are used for cooking, simultaneously or at different times. It can be used to control combustion in continuously operated recovery boilers such as

If the viscosity variation of the liquid is maintained within a suitable range, it is possible to adjust the droplet size simply by adjusting the temperature or nozzle opening.

It is also possible to mix liquids of different viscosities, adjust the nozzle opening, and heat them in the desired manner.
By combining cooling, it is also possible to adjust the droplet size, and all or some of the different control modalities can be used.

The present invention will be explained in detail with reference to Examples below.

Example FIG. 3 shows temporal changes in the viscosity and dry solid content of the waste steaming liquid (combustion liquid). In this example, the birch wood-based steaming waste liquid and the pine wood-based cooking waste liquid are fed into the same container at intervals as shown.

In the figure, A represents dry solid content. C represents the effluent viscosity before the mixing tank in which the flue dust recovered by the electrostatic precipitator from the flue gas is mixed with the effluent. This flue dust mainly consists of Na ₂ SO ₄ ;
Contains some Na ₂ CO ₃ . Such flue dust streams can amount to more than 10% of the effluent stream, so when this salt is mixed with the effluent, the viscosity of the mixture varies considerably. Moreover, the amount and composition of flue dust from electrostatic precipitators is not constant. As a result, the viscosity of the waste liquid after the mixing tank in which the salts are mixed constantly fluctuates as shown in B.

If the combustion liquid whose viscosity changes greatly in this way is supplied as it is to the liquid nozzle of the recovery boiler, combustion turbulence will occur in the recovery boiler.

In this example, immediately before supplying a combustion liquid with large viscosity fluctuations like B to the recovery boiler,
By continuously measuring the viscosity using a viscometer and preheating the combustion liquid, the viscosity can be adjusted and maintained at the set value D shown in the figure, and the droplet size suitable for combustion in the recovery boiler can be achieved. was able to give.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between viscosity and dry solids content for the same liquid sample. Figure 2 is a graph showing the relationship between viscosity and dry solids content for the same liquid sample. Figure 2 is a liquid using birch wood with a different dry solids content (region A).
and FIG. 3 is a graph showing the change in dry solid content and viscosity of the combustion liquid over time in an example of the present invention.

Claims (1)

[Claims] 1. When a combustion liquid whose chemical and physical consistency varies is supplied to a recovery boiler, the viscosity of the combustion liquid supplied to the recovery boiler is measured at least immediately before supply, Using this viscosity value as a direct basis, the droplet size of the combustion liquid supplied to the recovery boiler can be controlled by adjusting the opening of the combustion liquid supply nozzle, the supply pressure and/or the viscosity of the combustion liquid supplied. A method for controlling liquid combustion in a recovery boiler, characterized by adjusting the size to a suitable size. 2. The method of claim 1, wherein the viscosity of the combustion liquid supplied to the recovery boiler is adjusted by mixing it with a combustion liquid having a higher or lower viscosity. 3. The method of claim 1, wherein the viscosity of the combustion liquid supplied to the recovery boiler is adjusted by cooling or heating the combustion liquid. 4. A method as claimed in claim 1, in which liquids with different viscosities are mixed in order to adjust the viscosity and the combustion liquid fed to the recovery boiler is cooled or heated. 5. A method according to claims 1 to 4, in which the viscosity of the combustion liquid is maintained between two limiting values. 6. Claim for maintaining the viscosity of the combustion liquid supplied to the recovery boiler between two limiting values and for controlling the heating and cooling of the combustion liquid depending on the rate at which the viscosity changes between said limiting values. The method according to item 3 or 4.