JP2894195B2 - How to prevent chip bin waste gas explosion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing explosion of waste gas from a chip bin. More specifically, the present invention relates to a method for introducing waste steam from a digestion process into a chip bin to preheat the chips and to discharge gas from the chip bin. And methods for reliably preventing explosions.

[0002]

2. Description of the Related Art As is well known, in a digestion process, chips (small pieces of wood) are paid out by a conveyor and stored in a chip bin. In recent years, for the purpose of energy conservation, waste steam (pressure of about 0.2 kg / cm ² ) generated in the digestion process is introduced into a chip bin to preheat chips, and the chip bin has been developed and widely used (this chip bin is called a high brabin). There).

[0003]

As described above, the waste steam in the digestion step is used for preheating the chips in the chip bin, and thus is effective in energy saving measures. Hydrogen sulfide (H ₂ S), methyl mercaptan (MeSH), methyl sulfide (Me ₂ S), methyl disulfide (Me ₂ S ₂ ) (where Me is a methyl group)
In addition, various combustible gases such as turpentine (C ₁₀ H ₁₆ ) (hereinafter collectively referred to as TRS) are included.

[0004] Most of this TRS is a reducing odor gas, which is deodorized by burning the waste gas in the chip bin in a combustion step. However, the TRS concentration of the waste gas discharged from the chip bin increases. When the explosion limit is exceeded, the explosion accident occurs during the combustion process, which is dangerous in terms of safety measures, and there are various problems such as damage to equipment.

However, until now, no means has been elucidated for preventing explosion that occurs when introducing waste steam into the chip bin, and it has been difficult to avoid the risk of explosion. The present inventor has studied the explosion of the waste gas in the chip bin, and as a result, ascertained that fluctuations in the internal volume of the chip in the chip bin and fluctuations in the volume of the waste steam portion are the main factors, thereby achieving the present invention.

[0006]

According to a first aspect of the present invention, there is provided a method for preheating chips by introducing waste steam from a digestion step into a chip bin, the method comprising the steps of: The chip level in the chip bin is 50
%, The introduction of waste steam in the digestion process into the chip bin is cut off or reduced to prevent the explosion of waste gas from the chip bin.

Further, a second invention is a method for preheating chips by introducing waste steam of a cooking step into a chip bin.
This is a method for preventing waste gas explosion of a chip bin, in which when the dispensing of chips in the chip bin is stopped, the introduction of waste steam in the digestion process to the chip bin is cut off or reduced.

Further, a third invention is a method for preheating chips by introducing waste steam of a cooking step into a chip bin.
This is a method for preventing waste gas explosion of a chip bin, which shuts off or reduces the introduction of waste steam in a digestion process to the chip bin when the concentration of combustible gas in the waste gas of the chip bin rises above a reference concentration.

Further, a fourth invention is a method for preheating chips by introducing waste steam of a digestion step into a chip bin, wherein when the waste gas temperature of the chip bin rises above a reference temperature, the digestion step for the chip bin is performed. This is a method for preventing explosion of waste gas in a chip bin that blocks or reduces the introduction of waste steam.

[0010]

The present invention is constructed as described above, and usually contains 50 to 80% of the chips in the chip bin, and replenishes the chips to the chip bin by a conveyor so as to be compatible with the operation of the cooking process. Chips are dispensed from chip bins and supplied to the cooking process.

In this case, in a steady state, the chip level in the chip bin and the volume of the waste steam portion hardly fluctuate, and the waste steam of the digestion step introduced therein can be smoothly introduced. If the volume of the section changes, the distribution of waste steam, air, TRS, etc. in the chip bin also changes.

[0012] Fluctuations in the chip level in the chip bin and the volume of the waste steam section occur in the following cases. 1) When the supply amount of the chip input conveyor falls below a certain amount. 2) When the tip level in the tip bin has dropped to 50% or less (generally, about 50 to 80% of the tip bin internal volume). 3) When the dispensing of chips from the chip bin is stopped.

As shown in FIG. 2, chips T are supplied from the upper part of the chip bin 1 and are deposited at about 50-80% of the internal volume, while chips T are discharged from the lower center of the chip bin 1. And sent to the cooking process. Further, waste steam is introduced from the lower side of the chip bin 1, and the waste gas in the chip bin 1 is discharged from the upper part of the chip bin 1 through the gap in the stack of chips.

The inventor has confirmed that the tip bin 1
An experiment was conducted on the temperature state and the gas distribution state in the steady state inside. That is, FIG. 3 shows the chip bin 1 of FIG.
2 shows an example of the internal gas temperature state sampled at the levels (a), (b), (c) and (d) of the chip bin 1 when waste steam from the digestion step is introduced (solid line). Is the summer season, and the two-dot chain line is the winter season). The summer temperature is 29.5 ° C, the tip temperature is 27 ° C, the winter temperature is 4 ° C, and the tip temperature is 7
° C and VP is the boiling point of methyl sulfide (Me ₂ S).

FIG. 4 shows the levels (a), (b), and (b) when waste steam from the digestion step is introduced into the chip bin 1 of FIG.
(c) and (d) show examples of the distribution state of water vapor, TRS and air in the chip bin 1 sampled respectively. In FIG. 4, ● represents steam% and ▲ represents TRS%.

Incidentally, the height of the cylindrical portion of the tip bin 1 is 12
1,000mm, diameter 4,570-4,840mm, sampling position (a)
Is 3,600 mm from the upper edge of the cylinder, (b) is 2,000 mm below (a),
(c) is 2,000 mm below (b), and (d) is 2,0 mm below (c).
00mm below. Note that the size of the tip bin is not particularly limited, and it can be considered that various sizes have the tendency shown in FIGS.

As apparent from FIG. 3, the gas temperature of the level in the tip bin 1 is 98.degree.
5 ° C, but drops rapidly from level (b)
It is about 30 ° C. However, the sharp rise in the temperature of the waste gas in the chip bin at the time of discharge is due to a change in the distribution of waste steam, air, TRS, and the like in the steady state chip bin, and therefore, it is necessary to measure the temperature. .

As shown in FIG. 4, the tip bin 1
In a steady state, waste steam of the digestion process is introduced from below, and air is introduced from above and circulates and diffuses. Therefore, most of the waste steam introduced from below the chip bin 1 is inside the chip bin 1. Contacted with chip T and aggregated, chip bin 1
Below (below level (d)), the proportion of steam is high.

Further, since air is introduced from the upper part of the chip bin 1, the proportion of air is high at the uppermost part (level (a) or more), and TRS in the waste steam is removed from the voids of the deposited chips T by ( In this case, the porosity of the deposited chip layer is about 65%.) The TRS in the waste gas of the chip bin 1 is discharged at such a concentration that there is no danger of explosion.

However, as shown in the above 1) to 3), when the chip level and the volume of the waste steam portion fluctuate, if the waste steam of the digestion step is continuously introduced into the chip bin 1, the waste gas in the chip bin 1 becomes Since the gas retained inside is pushed up by the subsequent waste steam continuously introduced and discharged at a stretch, the distribution of the air, TRS and water vapor in a steady state collapses, as shown by a dotted line in FIG. It was found that the TRS concentration in the upper part of the chip bin was increased and sent to the combustion process, resulting in an explosion.

In addition, the temperature drops as in winter,
When the temperature of the chip supplied to the inside of the chip bin 1 is low, the boiling point of methyl sulfide (38
C), where methyl sulfide is condensed and liquefied and stays there, and subsequently introduced waste steam heats and evaporates the methyl sulfide and discharges it at once. It has been determined that an explosion occurs as a result of the high concentration being sent to the combustion process. Therefore, the temperature of the waste gas is based on 40 ° C.

Therefore, according to the present invention, when the chip level in the chip bin and the volume of the waste steam portion fluctuate due to the above items 1) to 3), the waste steam introduced from the digestion step is immediately stopped or reduced. This successfully prevented such an explosion. In particular, in the present invention, the risk of explosion can be reliably eliminated by using the TRS risk conversion concentration described below as the reference for the TRS concentration at which explosion may occur.

[0023]

FIG. 1 shows an embodiment of the present invention. The present invention will be described below with reference to the drawings. Chips T are supplied from a stock yard (not shown) to the inside of a chip bin 1 by a conveyor 2 and sent to a steaming vessel 5 via a chip meter 3 and a low-pressure feeder 4, and then are fed to a high-pressure infiltration vessel 6 and an upper portion of the digester 7. Sent and cooked.

On the other hand, black liquor K is extracted from the middle stage of the digester 7 and separated from the steam by the primary flash cyclone 8 and the secondary flash cyclone 9 in sequence. The waste steam of the secondary flash cyclone 9 It is introduced from the side to preheat the chips T in the chip bin 1.

The waste steam of the primary flash cyclone 8 is sent to a steaming vessel 5 below the chip bin 1 where the chips are preheated , and part of the waste steam is passed through the low pressure feeder 4 to the chip bin 1. The waste gas from the chip bin 1 is introduced from below and used for chip preheating, and the waste gas in the chip bin 1 is discharged from the upper discharge port P, merges with the exhaust system L in the digestion process at the point Q, and is sent to the combustion process.

On the other hand, the liquid separated from the gas by the primary flash cyclone 8 and the secondary flash cyclone 9 is sent to the chemical recovery step via the pre-evaporator 10. The exhaust gas from the steaming vessel 5 is used as a heating source for the pre-evaporator 10.

Table 1 shows an example of the measured concentrations of various gases constituting the TRS of the chip bin 1 and the explosive limit concentrations of these gases.

[0028]

[Table 1]

On the other hand, the explosive limit concentration of the TRS mixed gas is
It is said that Le Chatelier's law (formula below) holds.

(Equation 1)

From the results of the calculations in Table 1 and Equation 1, it is considered that the dangerous concentration of TRS at which the waste gas causes an explosion is about 34,000 ppm or more. However, in the present invention, the reliability of the TRS meter, operation management such as operation fluctuation, etc. In consideration of the above safety, as a concentration at which there is a risk of explosion during actual operation, a standard that is 1/3 or less, ie, 10,000 ppm, which is even more severe than the TRS concentration, is used as a reference.
The concentration is assumed to be S danger conversion concentration, and is controlled so as not to exceed this value.

When the chip level and the volume of the waste steam portion in the chip bin 1 shown in the above 1) to 3) fluctuate, the TRS
Since the concentration increases or the temperature of the waste gas rises (for example, 40 ° C. or higher), the TRS concentration and temperature in the waste gas are measured, and the waste steam of the secondary flash cyclone 9 and the waste of the low-pressure feeder 4 are removed depending on the situation. Stop or reduce the introduction of steam. The measurement of the waste gas in the chip bin 1 is performed between the discharge port P of the chip bin 1 and the confluence point Q with the discharge system L in the digestion process, and the TRS concentration is measured between the discharge point L and the combustion process further downstream from the confluence point Q. At any position.

In measuring the waste gas, the TRS concentration in the waste gas in the chip bin 1 and the temperature of the waste gas at that time may be measured at regular intervals. In this case, the measurement may be performed manually, but preferably, the TRS concentration and the temperature are continuously measured using an automatic measuring device. By such measurement, the TRS concentration in the waste gas from the chip bin 1 can be checked,
In addition, an increase in TRS concentration can be predicted from an increase in temperature, and the introduction of waste steam can be controlled, so that an explosion can be reliably prevented.

[0033]

As described above, according to the present invention, when the waste steam of the digestion process is introduced into the chip bin to preheat the chips, when the chip level in the chip bin and the volume of the waste steam portion fluctuate, or when the waste gas in the chip bin is changed. When the temperature rises and the TRS concentration in the waste gas from the chip bin is predicted to be equal to or higher than the TRS dangerous conversion concentration or becomes higher than the TRS dangerous conversion concentration, the waste steam in the digestion process into the chip bin is stopped. Or, since the weight is reduced, the explosion due to the introduction of waste steam into the chip bin can be reliably prevented, the chips in the chip bin can be preheated , and the operational safety can be secured. In addition, it can contribute to energy saving measures.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment for introducing waste steam into a chip bin.

FIG. 2 is a sectional view of an example of the inside of a chip bin.

FIG. 3 is an explanatory diagram of an example of an internal temperature state in FIG. 2;

FIG. 4 is an explanatory diagram of an example of a gas distribution state in FIG. 2;

[Explanation of symbols]

 1: Chip bin 2: Conveyor 3: Chip meter 4: Low pressure feeder 5: Steaming vessel 6: High pressure permeation vessel 7: Digester 8: Primary flash cyclone 9: Secondary flash cyclone 10: Pre-evaporator L: Exhaust system T: Chip

Claims (4)

(57) [Claims] 1. A method for preheating chips by introducing waste steam from a digestion step into a chip bin, wherein when the supply amount of chips into the chip bin becomes less than a certain amount or when the chip level in the chip bin becomes 50% or less. A method for preventing waste gas explosion in a chip bin, wherein the introduction of waste steam in the digestion step to the chip bin is cut off or reduced when the waste gas is lost. 2. A method for preheating chips by introducing waste steam from a digestion step into a chip bin, wherein when discharge of chips from the chip bin to the digestion step is stopped, introduction of waste steam from the digestion step to the chip bin is interrupted or performed. A method for preventing waste gas explosion of a chip bin, characterized by reducing the weight. 3. A method for preheating chips by introducing waste steam from a digestion step into a chip bin, wherein when the concentration of flammable gas in the waste gas in the chip bin rises above a reference concentration, the waste steam from the digestion step into the chip bin is provided. A method for preventing explosion of waste gas in a chip bin, comprising shutting off or reducing the introduction of waste gas. 4. A method for preheating chips by introducing waste steam from a cooking step into a chip bin, wherein when waste gas temperature of the chip bin rises above a reference temperature, introduction of waste steam from the cooking step to the chip bin is cut off or A method for preventing waste gas explosion of a chip bin, characterized by reducing the weight.