Steam drum water level control system of boiler single-chamber balancing container

Abstract

The invention relates to the technical field of boiler drum water level measurement, in particular to a drum water level control system of a boiler single-chamber balancing container, which comprises a drum and a water level measuring mechanism, a steam side sampling pipe and a water side sampling pipe are respectively fixed on the drum, and the water level measuring mechanism comprises a single-chamber balancing container and a differential pressure transmitter. The steam drum water level measuring process comprises the following steps that firstly, the pressure P in a steam drum, the temperature T1 of a reference water column in a positive pressure communicating pipe and the temperature T2 in the steam drum are obtained; 2, the density rho1 of a reference water column in the positive pressure communicating pipe is obtained; the density rho 2 of saturated water in the steam pocket and the density rho 3 of saturated steam in the steam pocket; 3, judging whether the temperature T2 in the steam drum is greater than 80 DEG C or not, if so, executing the step 4, and if not, executing the step 5; 4, performing thermal compensation calculation; and 5, carrying out cold-state calculation. The steam drum water level can be accurately measured, and the boiler operation stability is guaranteed.

Description

Technical Field

[0001] This invention relates to the technical field of boiler drum water level measurement, specifically to a boiler drum water level control system for a single-chamber balance vessel. Background Technology

[0002] A boiler is an energy conversion device that converts the chemical or electrical energy in fuel into thermal energy and outputs steam, high-temperature water, or organic heat carriers with a certain amount of thermal energy. A boiler consists of two main parts: the "boiler" and the "furnace." The "boiler" refers to the steam-water flow system, including the boiler drum, headers, water-cooled walls, and convective heating surfaces, which is the heat-absorbing part of the heat exchange equipment. The "furnace" refers to the fuel combustion space and flue gas flow system, including the furnace, convective flue, and chimney, which is the heat-releasing part of the heat exchange equipment.

[0003] The steam drum, also known as the boiler drum, is a cylindrical pressure vessel in a water-tube boiler used for steam-water separation, steam purification, forming a water circulation loop, and storing boiler water. Maintaining the water level in the steam drum within a certain range is essential for ensuring the safe operation of the boiler. If the water level in the steam drum is too high, it directly affects the steam-water separation effect, increasing the humidity and salt content of the saturated steam and reducing its quality. If the water level in the steam drum is too low, it disrupts the natural steam-water circulation of the boiler, causing the water-cooled wall tubes to burn out, and in severe cases, even tube rupture. Therefore, measuring and controlling the water level in the steam drum is a crucial step in ensuring the stable and safe operation of the boiler, preventing safety accidents caused by abnormal water levels.

[0004] like Figure 1 As shown, conventional steam drum water level measuring instruments mostly use an external balancing container (such as a single-chamber balancing container 3). One end of the single-chamber balancing container 3 is connected to the steam side sampling pipe 2 of the boiler, and the other end of the single-chamber balancing container 3 is connected to the positive pressure end 5 of the differential pressure transmitter through the positive pressure connecting pipe 4. The negative pressure end 6 of the differential pressure transmitter is connected to the water side sampling pipe 8 of the steam drum through the negative pressure connecting pipe 7, so that the differential pressure transmitter can measure the pressure difference between the water side and the steam side of the steam drum and transmit the difference value to the DCS system. After the system converts the value, the liquid level height inside the steam drum can be obtained.

[0005] However, the single-chamber balance vessel exchanges heat with the outside environment. When the saturated steam 101 in the steam drum 1 enters the single-chamber balance vessel 3 from the steam-side sampling pipe 2, it will condense into saturated water. The surface water temperature of the reference liquid level 301 in the single-chamber balance vessel 3 is close to the saturation temperature. The positive pressure connecting pipe 4 has a certain height. As the height decreases, the water temperature in the reference liquid level 301 and the positive pressure connecting pipe 4 will also gradually decrease, making the reference water column in the reference liquid level 301 and the positive pressure connecting pipe 4 actually unsaturated water. The density of unsaturated water is different from that of saturated water. However, when the balance vessel calculates the actual water level in the steam drum, it usually treats the water in the reference water column as saturated water. This will make the calculated liquid column pressure of the reference water column inaccurate, resulting in the steam drum water level after system conversion not matching the actual level. This can easily cause the boiler interlock protection to fail to operate or to operate malfunction, affecting the stable operation of the boiler and causing serious economic losses and safety accidents. Summary of the Invention

[0006] This invention provides a steam drum water level control system for a single-chamber balance vessel of a boiler, which can solve the problem that the detected steam drum water level value does not match the actual value in the prior art, thus affecting the stable operation of the boiler and easily causing safety accidents.

[0007] This application provides the following technical solution: a steam drum water level control system for a single-chamber boiler balance vessel, including a steam drum and a water level measuring mechanism. A steam-side sampling pipe and a water-side sampling pipe are respectively fixed on the steam drum. The water level measuring mechanism includes a single-chamber balance vessel and a differential pressure transmitter connected between the steam-side sampling pipe and the water-side sampling pipe.

[0008] The end of the single-chamber balance vessel furthest from the steam drum is connected to the positive pressure end of the differential pressure transmitter via a positive pressure connecting pipe. The water-side sampling pipe is connected to the negative pressure end of the differential pressure transmitter via a negative pressure connecting pipe. A temperature transmitter is also installed on the positive pressure connecting pipe, and a pressure transmitter is installed on the negative pressure connecting pipe.

[0009] Beneficial effects:

[0010] The difficulty of this invention lies in the fact that, in actual production, the single-chamber balance vessel exchanges heat with the outside environment. When saturated steam from the steam drum enters the single-chamber balance vessel, it condenses into saturated water. The surface water temperature of the reference liquid surface in the single-chamber balance vessel is close to the saturation temperature, and this water column is saturated water. However, the water temperature below the reference liquid surface in the single-chamber balance vessel, as well as the water temperature of the water column in the positive pressure connecting pipe below the single-chamber balance vessel, decreases with decreasing height, making this water column unsaturated water. The density of unsaturated water is different from that of saturated water, but conventional measurement methods usually ignore this point, directly treating both water columns as saturated water using theoretical formulas and calculating the actual water level in the steam drum based on the density of saturated water. This leads to a discrepancy between the calculated steam drum water level and the actual water level, which can easily cause the boiler's interlock protection to fail to operate or malfunction, resulting in serious economic losses and safety accidents. The system obtains the pressure of the steam drum (the pressure of saturated water and saturated steam in the steam drum is equal) through a pressure transmitter and the temperature of the positive pressure connecting pipe through a temperature transmitter to obtain the pressure and temperature of the reference water column. Based on a table showing the density of water as a function of temperature and pressure, the system obtains the density ρ2 of the saturated water in the steam drum and the density ρ3 of the saturated steam in the steam drum. This allows for real-time correction of the reference water column density at different temperatures and pressures based on the pressure in the steam drum, making the liquid column pressure of the reference water column closer to the actual pressure. After adopting this scheme, multiple comparisons between the actual water level displayed by the field water level gauge and the calculated water level displayed on the control system interface show that the maximum water level error between the two is within 0-20mm, while the maximum allowable error for the steam drum water level is 50mm. It is evident that the steam drum water level calculated by the scheme in this application is far below the maximum allowable error value, ensuring the safe and stable operation of the boiler and preventing safety accidents.

[0011] Furthermore, the steam drum water level control process includes the following steps:

[0012] Step 1: Obtain the pressure P inside the steam drum, the temperature T1 of the reference water column in the positive pressure connecting pipe, and the temperature T2 inside the steam drum, respectively.

[0013] Step 2: Based on the data obtained in Step 1, obtain the density ρ1 (Kg / m3) of the reference water column in the positive pressure connecting pipe; the density ρ2 (Kg / m3) of the saturated water in the steam drum; and the density ρ3 (Kg / m3) of the saturated steam in the steam drum.

[0014] Step 3: Determine if the temperature T2 inside the steam drum is greater than 80℃. If yes, proceed to step 4; otherwise, proceed to step 5.

[0015] Step 4: Perform thermal compensation calculations and output the results;

[0016] Step 5: Perform cold calculations and output the results.

[0017] Beneficial effects: Based on the temperature inside the steam drum, selectively using corresponding thermal compensation or cold-state calculation methods under different temperature conditions can more accurately reflect the water level inside the steam drum, improve the accuracy of steam drum water level control, effectively monitor and control the water level inside the steam drum, and ensure the stable operation of the steam system.

[0018] Furthermore, in step four of the steam drum water level control process, the thermal compensation calculation formula is as follows:

[0019] Δh=-1 / 4*(-4ρ1L+ρ1m-ρ2m+4H0ρ2+4ρ3L-4H0ρ3+4*D*ΔP) / (ρ2-ρ3);

[0020] h = Δh + H0;

[0021] In the formula, m is the distance between the reference liquid level in the single-chamber balance vessel and the lower surface of the horizontal section of the positive pressure connecting pipe, Δh is the difference between the actual water level in the steam drum and the normal operating water level in the steam drum (mm), H0 is the distance between the normal operating water level in the steam drum and the center of the water-side sampling pipe (mm), L is the distance between the reference liquid level in the single-chamber balance vessel and the center of the water-side sampling pipe (mm), D is the unit conversion factor, ΔP is the differential pressure value (Pa) corresponding to the water level in the steam drum, and h is the distance between the actual water level in the steam drum and the center of the water-side sampling pipe (mm).

[0022] Beneficial effects: Thermal compensation calculation is used to perform measurement calculations under standard operating conditions of the steam drum. The calculation is based on the actual density of the reference water column, avoiding the influence of thermal effects on the actual pressure of the reference water column. This makes the measurement of steam drum water level more accurate and improves the precision of steam drum water level control.

[0023] Furthermore, in step five of the steam drum water level control process, the cold-state calculation formula is as follows:

[0024] Δh=-(-Lρ1+H0ρ1+DΔP) / ρ1;

[0025] h = Δh + H0.

[0026] Beneficial effects: Cold-state calculation is performed when the steam drum is in a non-standard operating state to measure and calculate the water level. At this time, the density in the reference water column is less affected by the thermal effect, which can simplify the calculation process, improve the system calculation efficiency, and thus improve the accuracy of steam drum water level measurement and control.

[0027] Furthermore, the temperature transmitter, pressure transmitter, and differential pressure transmitter are all electrically connected to the steam drum water level gauge DCS system.

[0028] Beneficial effects: The steam drum water level gauge DCS system can analyze and process the data obtained from the temperature transmitter, pressure transmitter and differential pressure transmitter, which is helpful in calculating the actual water level in the steam drum.

[0029] Furthermore, a temperature sensor is also installed inside the steam drum.

[0030] Beneficial effect: The temperature sensor is used to measure the temperature T2 inside the steam drum, which makes it easy to obtain the density of saturated water and saturated steam inside the steam drum based on T2 and the pressure P inside the steam drum.

[0031] Furthermore, the distance m between the reference liquid level of the single-chamber equilibrium container and the lower surface of the horizontal section of the positive pressure connecting pipe is equal to twice the diameter of the horizontal section of the positive pressure connecting pipe.

[0032] Beneficial effects: Setting m to twice the diameter of the horizontal section of the positive pressure connecting pipe helps to simplify the thermal compensation formula during calculation and improves the calculation efficiency of the steam drum water level gauge DCS system.

[0033] Furthermore, in step five of the steam drum water level measurement process, the h calculated in the cold state is the water level when the boiler equipment is not running or when the water in the steam drum has not reached the saturation temperature.

[0034] Beneficial effect: Calculating the actual water level when the boiler equipment is not running helps to select the appropriate installation height based on the water level in the steam drum when changing the installation water level. Attached Figure Description

[0035] Figure 1 This is the front view of a regular balanced container.

[0036] Figure 2 This is the front view of the present invention.

[0037] Figure 3 This is a logic block diagram of the present invention. Detailed Implementation

[0038] The following detailed description illustrates the specific implementation method:

[0039] The markings in the accompanying drawings include: steam drum 1, saturated steam 101, saturated water 102, steam-side sampling tube 2, single-chamber equilibrium vessel 3, reference liquid level 301, positive pressure connecting tube 4, positive pressure end 5, negative pressure end 6, negative pressure connecting tube 7, and water-side sampling tube 8.

[0040] Example 1

[0041] like Figure 1-3As shown, the boiler single-chamber balance vessel steam drum water level control system includes a steam drum 1 and a water level measuring mechanism. The steam drum 1 is connected to a steam-side sampling pipe 2 and a water-side sampling pipe 8 respectively. The water level measuring mechanism includes a single-chamber balance vessel 3 connected between the steam-side sampling pipe 2 and the water-side sampling pipe 8 and a differential pressure transmitter.

[0042] The end of the single-chamber balance vessel 3 furthest from the steam drum 1 is connected to the positive pressure end 5 of the differential pressure transmitter via a positive pressure connecting pipe 4. The water-side sampling pipe 8 is connected to the negative pressure end 6 of the differential pressure transmitter via a negative pressure connecting pipe 7. A temperature transmitter is installed on the positive pressure connecting pipe 4, and a pressure transmitter is installed on the negative pressure connecting pipe 7. A temperature sensor is also installed inside the steam drum 1. The temperature transmitter, pressure transmitter, and differential pressure transmitter are all electrically connected to the steam drum water level gauge DCS system.

[0043] The steam drum water level measurement process is performed using the steam drum water level gauge DCS system, and includes the following steps:

[0044] Step 1: Obtain the pressure P inside the steam drum 1, the temperature T1 of the reference water column in the positive pressure connecting pipe 4, and the temperature T2 inside the steam drum 1 respectively. The pressure P inside the steam drum 1 is obtained through a pressure transmitter, the temperature T1 of the reference water column in the positive pressure connecting pipe 4 is obtained through a temperature transmitter, and the temperature T2 inside the steam drum 1 is obtained through a temperature sensor inside the steam drum 1.

[0045] Step 2: Based on the data obtained in Step 1, obtain the density ρ1 (Kg / m3) of the reference water column in the positive pressure connecting pipe 4, the density ρ2 (Kg / m3) of the saturated water in the steam drum 1, and the density ρ3 (Kg / m3) of the saturated steam in the steam drum 1 according to the "DL / T839-2003 Field Test Method for Performance of Large Boiler Feed Pumps".

[0046] Step 3: Determine if the temperature T2 inside the steam drum 1 is greater than 80℃. If yes, proceed to step 4; otherwise, proceed to step 5. If the temperature T2 inside the steam drum is greater than 80℃, it indicates that the boiler is operating in a hot state. Use the heat compensation formula from step 4 to calculate the steam drum water level. Otherwise, it is assumed that the boiler equipment is not running or the water inside the steam drum has not reached the saturation temperature. Use the cold state formula from step 5 to calculate the steam drum water level.

[0047] Step 4: Perform thermal compensation calculations and output the results. The thermal compensation calculation formula is as follows:

[0048] Δh=-1 / 4*(-4ρ1L+ρ1m-ρ2m+4H0ρ2+4ρ3L-4H0ρ3+4DΔP) / (ρ2-ρ3)

[0049] h = Δh + H0;

[0050] In the formula, m is the distance between the reference liquid level 301 in the single-chamber balance vessel 3 and the lower surface of the horizontal section of the positive pressure connecting pipe 4, Δh is the difference (mm) between the actual water level in the steam drum and the normal operating water level in the steam drum, H0 is the distance (mm) between the normal operating water level in the steam drum and the center of the diameter of the water-side sampling pipe 8, L is the distance (mm) between the reference liquid level 301 in the single-chamber balance vessel 3 and the center of the diameter of the water-side sampling pipe 8, D is the unit conversion factor, ΔP is the differential pressure value (Pa) corresponding to the water level in the steam drum, and h is the distance (mm) between the actual water level in the steam drum and the center of the center of the water-side sampling pipe 8. Furthermore, the distance m between the reference liquid level 301 in the single-chamber balance vessel 3 and the lower surface of the horizontal section of the positive pressure connecting pipe 4 is equal to twice the diameter of the horizontal section of the positive pressure connecting pipe 4, which simplifies the calculation formula and improves the calculation efficiency.

[0051] Step 5: Perform cold calculations and output the results. The cold calculation formula is as follows:

[0052] Δh=-(-Lρ1+H0ρ1+DΔP) / ρ1

[0053] h = Δh + H0.

[0054] The calculation method of this system is as follows:

[0055] Thermal compensation calculation:

[0056] Calculation principle: The differential pressure value of the steam drum water level detected by the differential pressure transmitter = water pressure from the reference liquid level 301 in the single-chamber balance vessel 3 to the center of the diameter of the horizontal section of the positive pressure connecting pipe 4 + reference water column pressure between the center of the diameter of the horizontal section of the positive pressure connecting pipe 4 and the center of the diameter of the water-side sampling pipe 8 - saturated water pressure between the center of the diameter of the water-side sampling pipe 8 in the steam drum and the normal water level of the steam drum - saturated water pressure between the normal water level of the steam drum and the actual water level of the steam drum - saturated steam pressure between the actual water level in the steam drum 1 and the reference liquid level 301 in the single-chamber balance vessel 3;

[0057] Therefore, the formula is established as follows:

[0058] DΔP=ρ2m / 4+ρ1(Lm / 4)—ρ2H0—ρ2Δh—ρ3(L—H0—Δh)

[0059] h=Δh+H0

[0060] After the formula is transformed, Δh in step four of the steam drum water level measurement process can be obtained, and then the actual water level h in the steam drum can be calculated. Since the surface water temperature of the reference liquid surface 301 in the single-chamber balance container 3 is close to the saturation temperature in the steam drum 1, the water pressure from the reference liquid surface 301 in the single-chamber balance container 3 to the center of the horizontal section of the positive pressure connecting pipe 4 is calculated using the density ρ2 of saturated water. The reference water column between the center of the horizontal section of the positive pressure connecting pipe 4 and the center of the water-side sampling pipe 8 gradually decreases in temperature as the height decreases, so the pressure of this reference water column is calculated using ρ1. Furthermore, when measuring the height of each liquid surface, the center of the diameter of each connecting pipe is used to measure the height, which can reduce errors and ensure accuracy.

[0061] Cold calculation:

[0062] The cold-state calculation assumes the boiler equipment is not running or the temperature inside the steam drum has not reached saturation temperature. Therefore, there is no saturated steam pressure inside the steam drum, and the density ρ1 of the reference water column in the positive pressure connecting pipe 4 is equal to the density ρ2 of the saturated water inside the steam drum. Then:

[0063] The differential pressure value of the steam drum water level detected by the differential pressure transmitter = the reference water column pressure between the reference liquid level 301 in the single-chamber balance vessel 3 and the center of the diameter of the water-side sampling pipe 8 - the saturated water pressure between the center of the diameter of the water-side sampling pipe 8 in the steam drum and the normal water level in the steam drum - the saturated water pressure between the normal water level in the steam drum and the actual water level in the steam drum, that is:

[0064] DΔP=ρ1L—ρ1H0—ρ1Δh

[0065] h=Δh+H0

[0066] After the formula is transformed, Δh in step five of the steam drum water level measurement process can be obtained, and then the actual water level h in the steam drum can be calculated.

[0067] The following table shows the water level error data after comparing the conventional water level measurement system with the water level measurement system of this invention:

[0068] Actual measurement error of steam drum water level Maximum permissible error of steam drum water level Frequency of water level deviation Conventional water level measurement system 0-30mm 50mm 2-3 times per month on average Water level measurement system of the present invention 0-20mm 50mm No deviations were found

[0069] The data above shows that when using the existing conventional water level measurement system to monitor the water level of the steam drum, the error range between the measured water level and the actual water level is 0-30mm. Although this usually does not exceed the maximum allowable error of 50mm, there are still occasional instances of water level deviation averaging 2-3 times per month. However, using the water level measurement system of this invention, the error range between the measured water level and the actual water level is 0-20mm. This not only results in a smaller error compared to the original conventional water level measurement system, but also shows no instances of water level deviation exceeding the allowable error. This indicates that the measurement system of this invention not only has higher measurement accuracy and smaller error, but also good stability.

[0070] The above are merely embodiments of the present invention. The invention is not limited to the fields covered by these embodiments, and common knowledge regarding specific structures and characteristics is not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of this utility model. These modifications will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A boiler single-chamber balance vessel steam drum water level control system, comprising a steam drum and a water level measuring mechanism, wherein a steam-side sampling pipe and a water-side sampling pipe are respectively fixed on the steam drum, and the water level measuring mechanism comprises a single-chamber balance vessel and a differential pressure transmitter connected between the steam-side sampling pipe and the water-side sampling pipe; characterized in that: The end of the single-chamber balance vessel furthest from the steam drum is connected to the positive pressure end of the differential pressure transmitter via a positive pressure connecting pipe. The water-side sampling pipe is connected to the negative pressure end of the differential pressure transmitter via a negative pressure connecting pipe. A temperature transmitter is also installed on the positive pressure connecting pipe, and a pressure transmitter is installed on the negative pressure connecting pipe.

2. The boiler drum water level control system for a single-chamber balance vessel according to claim 1, characterized in that: The steam drum water level control process includes the following steps: Step 1: Obtain the pressure P inside the steam drum, the temperature T1 of the reference water column in the positive pressure connecting pipe, and the temperature T2 inside the steam drum, respectively. Step 2: Based on the data obtained in Step 1, obtain the density ρ1 (Kg / m3) of the reference water column in the positive pressure connecting pipe; the density ρ2 (Kg / m3) of the saturated water in the steam drum; and the density ρ3 (Kg / m3) of the saturated steam in the steam drum. Step 3: Determine if the temperature T2 inside the steam drum is greater than 80℃. If yes, proceed to step 4; otherwise, proceed to step 5. Step 4: Perform thermal compensation calculations and output the results; Step 5: Perform cold calculations and output the results.

3. The boiler drum water level control system for a single-chamber balance vessel according to claim 2, characterized in that: In step four of the steam drum water level control process, the thermal compensation calculation formula is as follows: Δh=-1 / 4*(-4ρ1L+ρ1m-ρ2m+4H0ρ2+4ρ3L-4H0ρ3+4*D*ΔP) / (ρ2-ρ3); h = Δh + H0; In the formula, m is the distance between the reference liquid level in the single-chamber balance vessel and the lower surface of the horizontal section of the positive pressure connecting pipe, Δh is the difference between the actual water level in the steam drum and the normal operating water level in the steam drum (mm), H0 is the distance between the normal operating water level in the steam drum and the center of the water-side sampling pipe (mm), L is the distance between the reference liquid level in the single-chamber balance vessel and the center of the water-side sampling pipe (mm), D is the unit conversion factor, ΔP is the differential pressure value (Pa) corresponding to the water level in the steam drum, and h is the distance between the actual water level in the steam drum and the center of the water-side sampling pipe (mm).

4. The boiler drum water level control system for a single-chamber balance vessel according to claim 3, characterized in that: In step five of the steam drum water level control process, the cold-state calculation formula is as follows: Δh=-(-Lρ1+H0ρ1+DΔP) / ρ1; h = Δh + H0.

5. The boiler drum water level control system for a single-chamber balance vessel according to claims 1-4, characterized in that: The temperature transmitter, pressure transmitter, and differential pressure transmitter are all electrically connected to the steam drum water level gauge DCS system.

6. The boiler drum water level control system for a single-chamber balance vessel according to claim 5, characterized in that: A temperature sensor is also installed inside the steam drum.

7. The boiler drum water level control system for a single-chamber balance vessel according to claim 6, characterized in that: The distance m between the reference liquid level of the single-chamber equilibrium container and the lower surface of the horizontal section of the positive pressure connecting pipe is equal to twice the diameter of the horizontal section of the positive pressure connecting pipe.

8. The boiler drum water level control system for a single-chamber balance vessel according to claim 7, characterized in that: In step five of the steam drum water level measurement process, the h calculated in the cold state is the water level when the boiler equipment is not running or when the water in the steam drum has not reached the saturation temperature.

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