CN201382908Y - An online measuring device for the black liquor concentration of the evaporator used for papermaking alkali recovery - Google Patents

Abstract

The utility model relates to the field of papermaking, and discloses an online measuring device for the black liquor concentration of an evaporator used for papermaking alkali recovery. It includes: a measuring cylinder, the bottom inlet of which is connected to the bottom of the evaporator through pipes, and the upper outlet is respectively connected to the upper part of the evaporator through pipes, and the side wall between the bottom inlet and the upper outlet of the measuring cylinder is provided with an upper measurement point and The lower measuring point; a sampling pump, set between the bottom inlet of the measuring cylinder and the bottom of the evaporator, provides boiling black liquor to the measuring cylinder; the first temperature sensor detects the temperature _T1 of the black liquor at the upper measuring point; the second A temperature sensor to detect the black liquor temperature T ₂ at the lower measurement point; a differential pressure transmitter to detect the pressure difference ΔP between the upper and lower measurement points; a signal processing unit to detect the black liquor temperature T ₁ at the upper measurement point, and to measure the lower The black liquor temperature T ₂ at the point and the pressure difference ΔP between the upper and lower measurement points are calculated and output to the effective black liquor concentration of the evaporator.

Description

An online measuring device for the black liquor concentration of the evaporator used for papermaking alkali recovery

technical field

The utility model relates to the field of papermaking alkali recovery, in particular to an on-line measuring device for the black liquor concentration of an evaporator used for papermaking alkali recovery.

Background technique

The main task of the paper industry alkali recovery wheat straw pulp black liquor evaporation process is to concentrate the dilute black liquor with a concentration of about 10% from the washing section to about 45% thick black liquor through a multi-effect evaporator, and then send it to the combustion section Follow up. Evaporators mainly include long-tube rising-film evaporators and plate-type falling-film evaporators. Chinese enterprises generally adopt the form of "two plates and three tubes", that is, the I and II effects adopt the plate type and the III, IV, and V effects adopt the tube type. Enterprises use five-effect or seven-effect full-plate evaporators.

In the black liquor solids produced by the wheat straw alkaline pulping process, the inorganic matter accounts for about 30-35%, and the organic matter accounts for about 65-70%. The concentration of black liquor is determined by the amount of solids contained in it, which directly affects the operating efficiency and operating costs of the equipment in the subsequent alkali recovery and combustion section, and must be strictly controlled.

Due to the complex composition of black liquor solids, it is very difficult to accurately measure online, and no direct measuring instrument has yet been developed in China. Although foreign countries (such as Metso of Finland) have launched online direct measuring instruments, the price is high, exceeding 300,000 euros.

At present, in the alkali recovery and evaporation section of papermaking enterprises, the black liquor concentration in the dilute black liquor tank and the concentrated black liquor tank is still measured manually by the original Baume meter method. Due to the difficulty of real-time online measurement of the black liquor concentration of each effect evaporator Due to reasons such as cost and cost, the effective black liquor concentration of each effect evaporator is not measured, which makes the concentration control of the concentrated black liquor in the evaporation section have the characteristics of large capacity and long lag time, and provides automatic control of the concentrated black liquor concentration in the entire evaporation section. bring great difficulty. Therefore, in engineering, the method of combining cascade and feed-forward compensation is often used to indirectly stabilize the concentration of concentrated black liquor. Concentration online fluctuation information.

Contents of the invention

In order to overcome the difficulty of online measurement of the black liquor concentration of each effect evaporator in the papermaking alkali recovery and evaporation process, the present invention provides an online measurement device for the black liquor concentration of the papermaking evaporator, which can calculate the boiling state through indirect measurement The black liquor concentration produced by each effect evaporator in the papermaking alkali recovery evaporation process is convenient for the automatic control of the black liquor concentration in the evaporation section, improves the operating efficiency of the papermaking process, and reduces operating costs.

In order to solve the above-mentioned technical problems, the utility model adopts the following technical proposals to achieve.

An online measuring device for the black liquor concentration of an evaporator for recovery of papermaking alkali, characterized in that it includes:

A measuring cylinder, the bottom inlet of which is connected to the bottom of the evaporator through pipes, and the upper outlet is respectively connected to the upper part of the evaporator through pipes, and the upper and lower measuring points are arranged on the side wall between the bottom inlet and the upper outlet of the measuring cylinder ;

A sampling pump, arranged between the bottom inlet of the measuring cylinder and the bottom of the evaporator, supplies boiling black liquor to the measuring cylinder;

The first temperature sensor detects the black liquor temperature T ₁ at the upper measuring point;

The second temperature sensor detects the black liquor temperature T ₂ at the lower measuring point;

A differential pressure transmitter to detect the pressure difference ΔP between the upper and lower measuring points;

The signal processing unit calculates and outputs the effective black liquor concentration of the evaporator according to the black liquor temperature T ₁ at the upper measurement point, the black liquor temperature T ₂ at the lower measurement point, and the pressure difference ΔP between the upper and lower measurement points.

According to the basic principle of thermodynamics, the phase law F=S-P+2, where F, S, and P represent the number of degrees of freedom, the number of components, and the number of phases, respectively. It can be proved that the black liquor system in the boiling state is a two-degree-of-freedom system, that is, there are three variables that can be changed: black liquor boiling temperature T, black liquor column pressure difference ΔP and black liquor concentration C, but the variables that can be changed independently are only 2. That is, objectively there are three relationships: C=f1(ΔP, T), T=f2(C, ΔP) and ΔP=f3(C, T), where fi(), i=1, 2, 3 represent the function relation.

The field data was obtained through a large number of experiments, and the field data was processed by the least square algorithm and Householder transformation, and the following measurement model was obtained: Be(T)=a ₁ (1-gH/ΔP)-a ₂ (T-15), Among them, T is the temperature (unit, ℃), which represents the boiling point of the black liquor, Be(t) is the black liquor concentration when the temperature is T (expressed in Baume degree here), and ΔP is the distance between the two measuring points of the test cylinder differential pressure (unit, KPa), H is the height difference between the two measuring points of the test cylinder (unit, m), a ₁ and a ₂ are correction coefficients, and the values obtained through identification are a ₁ =144.3, a ₂ = 0.052, g is the gravitational acceleration constant, and its value is 9.8m/s ² . For a certain measurement device, H is a constant, T=(T ₁ +T ₂ )/2, T ₁ and T ₂ represent the temperature detection values of the upper and lower ends of the test cylinder respectively, therefore, as long as ΔP is obtained online in real time, T ₁ and T ₂ , the concentration of the black liquor in the boiling state (ie Baume degrees) can be obtained in real time through the above measurement model.

Further improvement and characteristics of the present utility model are:

The signal processing unit includes a single-chip microcomputer, and a signal interface circuit connected with the single-chip microcomputer.

A one-way valve is arranged on the pipeline where the upper outlet of the measuring cylinder communicates with the upper part of the evaporator.

The top of the measuring cylinder is provided with an exhaust valve.

A flushing valve and a blowdown valve are connected in parallel at the bottom inlet of the measuring cylinder.

The bottom of the measuring cylinder is provided with a pulse eliminator, which is a stainless steel plate with a plurality of round holes.

The utility model can quickly calculate the black liquor concentration of each effect evaporator in real time by measuring the boiling temperature T of the black liquor online and the pressure difference ΔP of the black liquor column with a certain height difference. For real-time display, it can also be remotely transmitted to the distributed control system DCS in the form of 4-20mA current for display or to participate in online real-time control. Therefore, the utility model can not only quickly measure the concentration of black liquor produced by each effect evaporator in the boiling state, solve the difficulty of online measurement of this parameter, but also provide real-time monitoring of the concentration of black liquor produced by each effect evaporator and the advanced process The implementation of the control algorithm provides convenience, and at the same time, it can significantly improve the automation level of the evaporation process, improve the operating efficiency of the papermaking process, and reduce operating costs with a small increase in investment costs.

Description of drawings

Below in conjunction with accompanying drawing and specific embodiment the utility model is further described.

Figure 1 is a schematic diagram of the on-site connection of the measuring cylinder;

Fig. 2 is a schematic diagram of the measurement principle of the specific on-line measurement device and the composition and structure of the transmission device;

Fig. 3 is the specific circuit connection schematic diagram of Fig. 2;

Fig. 4 is a schematic diagram of the structure of the pulse canceller.

Detailed ways

Referring to Figure 1, the measuring cylinder L is made of a straight pipe with a diameter of 80mm-100mm and a length of 2m-3m. The specific length depends on the height of the evaporator and the site space. A sight glass 1 with a scale, and a pulse eliminator 2 is installed at the bottom of the measuring cylinder L; the bottom inlet of the measuring cylinder L is connected to the bottom of the evaporator through a pipeline, and a sampling valve V ₁ and a sampling pump B are sequentially installed in the middle of the pipeline; the measuring cylinder L Drain valve V ₂ and flushing valve V ₃ are also installed at the bottom inlet of the tube respectively; the upper outlet of the measuring cylinder L is connected to the upper part of the evaporator through a pipeline, and a drain valve V ₄ and a one-way valve V ₆ are installed in the middle of the pipeline in sequence; The top end of the barrel L is provided with an exhaust valve V ₅ . The black liquor from the evaporator enters the measuring cylinder L through the sampling pump B and the sampling valve _V1 , and then enters the evaporator through the drain valve _V4 and the one-way valve _V6 . In normal use, the sampling valve V ₁ and drain valve V ₄ are open, and the drain valve V ₂ , flushing valve V ₃ and exhaust valve V ₅ are closed; when cleaning and overhauling, the sampling valve V ₁ and drain valve V ₄ are closed , the blowdown valve V ₂ , the flushing valve V ₃ and the exhaust valve V ₅ cooperate with each other to complete the cleaning task of the measuring cylinder L. An upper measuring point and a lower measuring point are arranged between the bottom inlet and the upper outlet of the measuring cylinder L, and the spacing is fixed at H, generally 2m. The first temperature sensor detects the black liquor temperature T ₁ at the upper measurement point; the second temperature sensor detects the black liquor temperature T ₂ at the lower measurement point; a differential pressure transmitter P detects the pressure difference ΔP between the upper and lower measurement points .

Referring to Figure 2, in the specific on-line measurement device, the black liquor enters the measuring cylinder from the bottom of the evaporator through the sampling pump, and then flows back to the evaporator; the differential pressure signal ΔP (the pressure difference ΔP between the upper and lower measurement points) and the temperature signal T ₁ (black liquor temperature T ₁ at the upper measurement point) and T ₂ (black liquor temperature T ₂ at the lower measurement point) are transmitted to the central processing unit CPU through the signal interface circuit to calculate the Baume degree of the evaporator black liquor; The switch state signal of the valve on the periphery of the measuring cylinder and the running state signal of the sampling pump are also transmitted to the central processing unit CPU through the signal interface circuit, and the start and stop signal of the sampling pump and the switch signal of the valve sent by the CPU are sent to the corresponding pump through the signal interface circuit And valves to change their operation or switch state. The signal interface circuit receives the analog and digital signals from the on-site measurement sensing part, and sends them to the 89C552 CPU after processing. The digital signal sent by the CPU is converted into a 4-20mA signal by the signal interface circuit and sent to the peripheral equipment; 89C552 CPU is mainly used for receiving, processing and sending signals, and sending them to LED, CRT/LCD and other peripheral display devices for Baume degree transmission results display; 16-key numeric keyboard is used for physical quantity zero point, range, Baume degree measurement For the setting of parameters such as mathematical model expression coefficients and the definition of function keys; the 4.5-digit LED is used for local real-time display of Baume degree measurement results, and the CRT/LCD display is used for remote display of Baume degree measurement results.

Referring to Fig. 3, the chip 89C552 is a highly integrated 8-bit single-chip microcomputer with MCS-51 structure, which integrates 8K program memory, 256 RAMs, 8-way 8-bit A/D conversion, and two-way PWM output. Three-way A/D conversion design: the first and second temperature sensors and differential pressure transmitters enter the CPU through I/V conversion input P5.0, P5.1 and P5.2. Two-way D/A conversion design: PWM ₁ and PWM ₀ output 4-20mA current through the keeper (LF398) and V/I conversion circuit, which is used to provide signal interface for other equipment or DCS. P1.0-P1.7 is the output of 8-way switching value, P2.0-P2.7 is the input of 8-way switching value, and P4.0-P4.7 completes the keyboard scanning circuit, forming 16 keys. ICM7211 is a 4-digit LCD drive circuit chip produced in the United States, YXY4501 is a 4.5-digit LCD display, its signal drive is driven by P0 port, P4.3-P4.7 is used as chip selection input line, and chip 6845 is used as CRT drive interface , Drive CRT/LCD display.

Referring to Fig. 4, the pulse eliminator is made of a stainless steel disc with a small circular hole with a diameter of 9-10mm. The diameter of the disc is 80-100mm, and it can cooperate with the above-mentioned measuring cylinder and be fixed at the lower part of the measuring cylinder to eliminate the flow pulse of black liquor entering the measuring cylinder through the sampling pump, so as to make the pressure measurement more accurate.

Claims (6)

1, a kind of papermaking alkali reclaims the on-line measurement device that goes out to imitate black liquid consistency with evaporator, it is characterized in that, comprising:

A measurement tube, its bottom inlet are by the bottom of pipeline connection evaporator, and its top outlet is communicated with the top of evaporator respectively by pipeline, and the sidewall between the bottom inlet of measurement tube and top export is provided with measurement point and following measurement point;

A sampling pump is arranged between the bottom of the bottom inlet of measuring tube and evaporator, provides the black liquor of boiling to measuring tube;

First temperature sensor, the black liquor temperature T of measurement point in the detection ₁

Second temperature sensor detects the black liquor temperature T of measurement point down ₂

A differential pressure transmitter detects the pressure differential deltap P between the measurement point up and down;

Signal processing unit is according to detecting the black liquor temperature T that goes up measurement point ₁, the following black liquor temperature T of measurement point ₂, the pressure differential deltap P between the measurement point up and down, calculate and the output evaporator goes out to imitate black liquid consistency.

2, a kind of papermaking alkali according to claim 1 reclaims the on-line measurement device that goes out to imitate black liquid consistency with evaporator, it is characterized in that described signal processing unit comprises single-chip microcomputer, and the signal interface circuit that is connected with single-chip microcomputer.

3, a kind of papermaking alkali according to claim 1 reclaims the on-line measurement device that goes out to imitate black liquid consistency with evaporator, it is characterized in that, the pipeline that described top outlet of measuring tube is communicated with the top of evaporator is provided with retaining valve.

4, a kind of papermaking alkali according to claim 1 reclaims the on-line measurement device that goes out to imitate black liquid consistency with evaporator, it is characterized in that, described measurement tube top is provided with vent valve.

5, a kind of papermaking alkali according to claim 1 reclaims the on-line measurement device that goes out to imitate black liquid consistency with evaporator, it is characterized in that, the described bottom inlet of measuring tube is parallel with flushing valve and blowoff valve.

6, a kind of papermaking alkali according to claim 1 reclaims the on-line measurement device that goes out to imitate black liquid consistency with evaporator, it is characterized in that described measurement tube bottom is provided with the pulse canceller, and described pulse canceller is the corrosion resistant plate that offers a plurality of circular holes.

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