Process for eliminating steam emptying

Abstract

The invention discloses a process for eliminating steam emptying. The process is characterized in that a device generates low-pressure condensed water; wherein one part directly enters a low-low pressure steam flash tank for flash evaporation; the other part is directly sent out; the low-pressure condensed water entering the low-low-pressure steam flash tank is subjected to flash evaporation to generate low-low-pressure steam obtained through flash evaporation and low-low-pressure condensed water obtained through flash evaporation; and the flashed low-low pressure steam enters a low-low pressure steam pipe network to be used by low-low pressure steam users, and the flashed low-low pressure condensed water is sent out. According to the invention, no excessive steam is discharged, so that no white steam is emitted, and the white steam is eliminated.

Description

Technical Field

[0001] This invention belongs to the fields of oil refining, petrochemicals, and chemical technology, and specifically relates to a process for eliminating steam venting. Background Technology

[0002] Oil refining, petrochemical, and chemical production processes consume significant amounts of energy, with steam being a primary energy source. Steam condensation generates substantial latent heat, meeting the heating demands of various production processes. Different pressure levels of steam are used for heating depending on the required temperature of the materials being heated. However, precisely setting the steam pressure for each heating material would lead to complex plant management, excessive pipelines, and high investment and operating costs. Therefore, most plants typically establish three different steam networks—high-pressure, medium-pressure, and low-pressure—for each unit and material to use. High-pressure is generally ≥3.5 MPaG, medium-pressure is generally 0.8-3.5 MPaG, and low-pressure is generally 0.3-0.8 MPaG. To improve steam utilization within each unit, condensate from different pressure levels can be flashed in flash tanks to produce a certain amount of lower-grade steam, achieving tiered utilization of flash steam and reducing the consumption of lower-grade steam. If the flashed amount of a certain grade of steam exceeds the usage, the excess flashed steam can be returned to the plant's steam network for use by other units.

[0003] In certain units, such as aromatics complexes and purified terephthalic acid units, some materials require a lower heat source than low-pressure steam. Direct heating with low-pressure steam would directly increase low-pressure steam consumption. Using low-pressure condensate for flash evaporation to generate low-pressure steam for these materials would not increase low-pressure steam consumption. Flash evaporation pressure is generally <0.3 MPaG, or even negative pressure. However, this creates another problem: matching the amount of low-pressure steam generated with the required amount. If the generated low-pressure steam is less than the required amount, low-pressure steam can be used to supplement it. If the generated low-pressure steam exceeds the required amount, the excess steam, due to the lack of a pipeline network and its very low pressure, cannot be transported to other units and must be vented, a phenomenon commonly known as "white steam." "White steam" causes the following problems: 1. Water loss due to venting; 2. Significant heat loss due to venting; 3. When the temperature is below zero, the vented steam will freeze on the ground, posing a safety hazard.

[0004] Chinese patent CN201694982U discloses a steam condensate recovery device, in which a heat exchanger is installed on the top of a steam condensate tank. When excess steam is generated in the flash tank, the excess steam is recovered and condensed by the heat exchanger. Although this patent has the function of condensing excess flash steam, it has the following problems:

[0005] 1. Excess steam enters the heat exchanger from the top of the flash tank, turns into condensate, and then returns to the flash tank. Steam and condensate flow in opposite directions within the heat exchanger. Regardless of whether the steam flows through the tube side or the shell side, the maximum steam volume and the maximum condensate volume occur simultaneously at the bottom of the heat exchanger. This increases the steam flow resistance and reduces the condensate removal speed, thus affecting the thickness of the liquid film on the heat exchange tubes. All of these factors will affect the heat exchanger's heat exchange efficiency. A heat exchanger that can completely condense steam when steam and condensate flow in the same direction cannot completely condense excess steam when installed at the top of the tank. This means that it is difficult to completely eliminate the "white steam" phenomenon, or more costs need to be invested to install a larger heat exchanger to eliminate the "white steam" phenomenon.

[0006] 2. Excess steam enters the heat exchanger from the top of the flash tank, turns into condensate, and then returns to the flash tank. Steam and condensate flow in opposite directions within the heat exchanger. Regardless of whether the steam flows through the tube side or the shell side, the maximum steam flow and the maximum condensate flow both occur simultaneously at the bottom of the heat exchanger, increasing steam flow resistance. The pressure at the top of the heat exchanger is lower than the flash tank pressure, and the steam condensation temperature is lower than the flash tank flashing temperature. After leaving the heat exchanger, the steam condensate drips directly to the bottom of the tank, without sufficient time and contact surface for heat exchange with the steam. This ultimately leads to a decrease in the water temperature at the bottom of the tank, which is detrimental to water utilization. Summary of the Invention

[0007] This invention provides a process for eliminating steam venting, thereby solving the "white steam" phenomenon in existing technologies and fundamentally eliminating venting steam.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A process for eliminating steam venting, characterized in that:

[0010] 1) The device produces high-grade condensate;

[0011] 2) The high-grade condensate produced in step 1) is divided into two parts, one part of which is directly flashed into the low-pressure steam flash tank; the other part is directly sent out.

[0012] 3) Step 2) The high-grade condensate entering the low-pressure steam flash tank is flashed to generate low-pressure flash steam and flashed low-pressure condensate;

[0013] 4) After the low-pressure flash steam from step 3) enters the low-pressure steam network for use by the low-pressure heat exchanger, it generates low-pressure condensate, which is sent out together with or separately from the low-pressure condensate from step 3) flash steam.

[0014] The present invention provides a process for eliminating steam venting, which is further characterized in that: the device refers to a device for materials that require a heat source lower than low-pressure steam, and the low-pressure steam flashed out of the low-pressure steam flash tank is more than the low-pressure steam heat exchanger requires.

[0015] The present invention provides a process for eliminating steam venting, which is further characterized in that: the high-grade condensate is one or more of high-pressure condensate, medium-pressure condensate, and low-pressure condensate.

[0016] The present invention provides a process for eliminating steam venting, which is further characterized in that: the high-grade condensate generated in the device is divided into two parts, each of which can be one or more streams of low-pressure condensate.

[0017] This invention provides a process for eliminating steam venting, further characterized in that: the high-grade condensate directly entering the low-pressure steam flash tank must ensure that the amount of low-pressure steam flashed in the low-pressure steam flash tank is equal to the amount of low-pressure steam required by the low-pressure steam heat exchanger. Without excess steam venting, there will be no "white steam," and the white steam is eliminated.

[0018] The present invention provides a process for eliminating steam venting, which is further characterized in that: the flow rate of high-grade condensate directly entering the low-pressure steam flash tank is controlled by the pressure of the low-pressure steam pipeline network or the pressure of the low-pressure steam flash tank.

[0019] The present invention provides a process for eliminating steam venting, which is further characterized in that: another portion of the high-grade condensate enters a condensate heat exchanger for heat exchange and is then sent out.

[0020] The present invention provides a process for eliminating steam venting, which is further characterized in that: another portion of the high-grade condensate enters the condensate heat exchanger for heat exchange and then enters the low-pressure steam flash tank, and the temperature after heat exchange is not higher than the saturation temperature corresponding to the flash pressure of the low-pressure steam flash tank.

[0021] The present invention provides a process for eliminating steam venting, further characterized in that: the cold source of the condensate heat exchanger is one or more of cooling water, hot water, and lithium bromide. The cold source of the condensate heat exchanger can also be one or more process materials whose heated temperature is lower than the low-pressure condensate temperature.

[0022] The present invention provides a process for eliminating steam venting, further characterized in that: a calculation module is set in the device DCS to perform feedforward control of the flow rate of high-grade condensate directly entering the low-pressure steam flash tank or another portion of the high-grade condensate directly discharged, and the calculation is performed according to the following steps:

[0023] 1) Measure or calculate the high-grade condensate flow rate W 进 ;

[0024] 2) Based on the high-grade condensate pressure, find the unit enthalpy H of the condensate from the steam property table. 进 ;

[0025] 3) Measure or calculate the low-pressure steam demand W出汽

[0026] 4) Based on the operating pressure of the low-pressure steam flash tank, find the enthalpy value H of the steam at the operating pressure of the flash tank from the steam property table. 出汽 Enthalpy of condensate H 出水 ;

[0027] 5) Calculate the required condensate flow rate Wpart to enter the low-pressure steam flash tank using the following formula.

[0028] W 部进 =W 出汽 / ((H 进 -H 出水 ) / (H 出汽 -H 出水 ))

[0029] 6) According to the calculated W 部进 Control the flow rate of high-grade condensate entering the low-pressure steam flash tank, or calculate W using the following formula. 不进 Control the flow rate of another portion of the high-grade condensate.

[0030] W 不进 =W 进 -W 部进

[0031] The present invention provides a process for eliminating steam venting, which is further characterized in that: the high-level condensate flow rate is controlled by a calculation module and the low-pressure steam network pressure or the low-pressure steam flash tank pressure in a cascade manner.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1) The problem of "white vapor" has been completely solved at its root, preventing the generation of white vapor;

[0034] 2) No water resources are wasted;

[0035] 3) It can realize heat utilization;

[0036] 4) Safety hazards have been eliminated;

[0037] 5) It can achieve intelligent operation. Attached Figure Description

[0038] Appendix Figure 1 This is a schematic diagram of the existing technology process;

[0039] Appendix Figure 2 This is a schematic diagram of a process flow for eliminating steam venting according to the present invention;

[0040] Appendix Figure 3 This is a schematic diagram of a steam venting process with heat exchange according to the present invention.

[0041] Appendix Figure 4 This is a schematic diagram of a steam venting process with a calculation module according to the present invention.

[0042] The attached diagram is labeled as follows: 1-Low-pressure condensate, 2-Low-pressure steam flash tank, 3-Low-pressure steam network, 4-Low-pressure flash steam, 5-Excess steam from flash, 6-Low-pressure heat exchanger (one or more units), 7-Low-pressure condensate from flash, 8-Low-pressure condensate, 9-Low-pressure condensate A, 10-Low-pressure condensate B, 11-Condensate heat exchanger, 13-Condensate control valve, 14-Hot water, 16-All low-pressure condensate, 17-Medium-pressure condensate, 18-High-pressure condensate, 19-Medium-pressure condensate A, 20-Medium-pressure condensate B, 21-High-pressure condensate A, 22-High-pressure condensate B. Detailed Implementation

[0043] The following is in conjunction with the appendix Figure 1-4 The implementation of the technical solution of the present invention will be further described.

[0044] Appendix Figure 1 This is a schematic diagram of the existing technology process. The low-pressure condensate 1 generated in the unit enters the low-pressure steam flash tank 2, producing low-pressure flash steam 4, excess flash steam 5, and low-pressure flash condensate. The low-pressure flash steam 4 enters the low-pressure steam network 3 and is condensed by one or more low-pressure heat exchangers 6 to produce low-pressure condensate 8, which returns to the low-pressure steam flash tank 2. Inside the tank, it mixes with the flashed low-pressure condensate to form all the low-pressure condensate 16, which is then discharged. To maintain the pressure in the low-pressure steam flash tank 2, the excess flash steam 5 is vented.

[0045] Example 1

[0046] As attached Figure 2 The diagram shown is a schematic of a steam venting process according to the present invention. The difference from the prior art is that the medium-pressure condensate 17 is divided into two parts, one part of which goes to the low-pressure steam flash tank and the other part is sent out.

[0047] Specifically as follows:

[0048] The medium-pressure condensate 17 is divided into two parts: medium-pressure condensate A19 and medium-pressure condensate B20. Medium-pressure condensate A19 goes to the low-pressure steam flash tank 2, and medium-pressure condensate B20 is sent out. The flow rate of medium-pressure condensate A19 is such that the amount of low-pressure flash steam 4 produced after flashing in the low-pressure steam flash tank 2 is equal to the amount of steam required by the low-pressure heat exchanger (one or more units) 6. Medium-pressure condensate A19 enters the low-pressure steam flash tank 2, producing low-pressure flash steam 4 and flashed low-pressure condensate. Low-pressure flash steam 4 enters the low-pressure steam network 3, and then enters the low-pressure heat exchanger (one or more units) 6 to condense and produce low-pressure condensate 8, which returns to the low-pressure steam flash tank 2. In the tank, it mixes with the flashed low-pressure condensate to form all the low-pressure condensate 16, which is then sent out. Since the flow rate of medium-pressure condensate A19 meets the requirement that the amount of low-pressure flash steam 4 generated after flashing in low-pressure steam flash tank 2 is equal to the amount of steam required by low-pressure steam heat exchanger (one or more units) 6, there is no excess steam to be released.

[0049] Example 2

[0050] As attached Figure 3 The diagram shown is a schematic of a steam venting process according to the present invention. The difference from the prior art is that the high-pressure condensate 18 is divided into two parts. One part is sent to the low-pressure steam flash tank under the pressure control of the low-pressure steam pipeline network, and the other part is sent out after heat exchange.

[0051] Specifically as follows:

[0052] High-pressure condensate 18 is divided into two parts: high-pressure condensate A21 and high-pressure condensate B22. High-pressure condensate A21 enters the low-pressure steam flash tank 2 through the condensate control valve 13 under the pressure control of the low-pressure steam network 3. High-pressure condensate B22 is sent out after heat exchange in the condensate heat exchanger 11. The cold source is hot water 14. High-pressure condensate A21 enters the low-pressure steam flash tank 2, generating low-pressure flash steam 4 and flashed low-pressure condensate 7. Low-pressure flash steam 4 enters the low-pressure steam network 3 and is completely condensed by the low-pressure steam heat exchanger (one or more units) 6 to generate low-pressure condensate 8. Flashed low-pressure condensate 7 and low-pressure condensate 8 are sent out separately. Since the flow rate of high-pressure condensate A21 meets the requirement that the amount of low-pressure flash steam 4 generated after flashing in low-pressure steam flash tank 2 is equal to the amount of steam required by low-pressure steam heat exchanger (one or more units) 6, there is no excess steam to be released.

[0053] Example 3

[0054] As attached Figure 4The diagram shown is a schematic of a steam venting process according to the present invention. The difference from the prior art is that the low-pressure condensate is divided into two parts. One part goes to the low-pressure steam flash tank, and its flow rate is controlled by the calculation module. The other part of the low-pressure condensate goes to the low-pressure steam flash tank after heat exchange. The temperature after heat exchange is not higher than the saturation temperature corresponding to the flash pressure of the low-pressure steam flash tank.

[0055] Specifically as follows:

[0056] Low-pressure condensate 1 is divided into two parts: low-pressure condensate A9 and low-pressure condensate B10. Low-pressure condensate A9 enters the low-pressure steam flash tank 2 under the control of condensate control valve 13 via a calculation module. Low-pressure condensate B10 enters the low-pressure steam flash tank 2 after heat exchange via condensate heat exchanger 11. The temperature after heat exchange is not higher than the saturation temperature corresponding to the flash pressure of the low-pressure steam flash tank. The cold source is hot water 14. Low-pressure condensate A9 enters the low-pressure steam flash tank. 2. Low-pressure flash steam 4 and flashed low-pressure condensate are generated. The low-pressure flash steam 4 enters the low-pressure steam network 3 and is completely condensed by the low-pressure heat exchanger (one or more units) 6 to produce low-pressure condensate 8, which returns to the low-pressure steam flash tank 2. In the tank, it mixes with the flashed low-pressure condensate and the low-pressure condensate B10 whose temperature after heat exchange is not higher than the saturation temperature corresponding to the flash pressure of the low-pressure steam flash tank, forming all the low-pressure condensate 16, which is then sent out. Since the flow rate of the low-pressure condensate A9 meets the requirement that the amount of low-pressure flash steam 4 generated after flashing in the low-pressure steam flash tank 2 is equal to the amount of steam required by the low-pressure steam heat exchanger (one or more units) 6, the low-pressure condensate B10 goes to the low-pressure steam flash tank 2 after heat exchange in the condensate heat exchanger 11. After heat exchange, the temperature is not higher than the saturation temperature corresponding to the flash pressure of the low-pressure steam flash tank, and no more steam is generated, so there is no excess steam to be released.

[0057] The calculation process of the calculation module is illustrated in the following example:

[0058] A certain plant produces 100 t / h of 0.5 MPaG low-pressure condensate and requires 3.6 t / h of 0.2 MPaG low-pressure steam. The plant is equipped with a low-pressure steam flash tank, operating at 0.2 MPaG. If all 100 t / h of the 0.5 MPaG low-pressure condensate enters the low-pressure steam flash tank, it will flash to produce 5.04 t / h of 0.2 MPaG low-pressure steam. Of this, 3.6 t / h will be used in the plant's low-pressure steam network. Only 1.44 t / h of steam (5.04 - 3.6 = 1.44 t / h) needs to be vented to maintain the pressure at 0.2 MPaG.

[0059] Enable the calculation module and calculate the low-pressure condensate flow control point entering the low-pressure steam flash tank according to the following path:

[0060] 1. Measure or calculate the low-pressure condensate flow rate W 进 =100t / h

[0061] 2. Based on the low-pressure condensate pressure of 0.5 MPaG and saturation temperature of 158.83℃, refer to the water vapor property table to find the unit enthalpy H of the condensate. 进 = 670.501 kJ / kg;

[0062] 3. Measure or calculate the low-pressure steam demand W 出汽 = 3.6t / h

[0063] 4. Based on the flash tank operating pressure of 0.2 MPaG and saturation temperature of 133.523℃, refer to the steam property table to find the enthalpy H of the flash tank operating pressure steam. 出汽 =2724

[0064] KJ / KG, enthalpy of condensate H 出水 = 561.455 kJ / kg;

[0065] 5. Calculate the required condensate flow rate Wpart to enter the low-pressure steam flash tank using the following formula.

[0066] W 部进 =W 出汽 / ((H 进 -H 出水 ) / (H 出汽 -H 出水 ))

[0067] =3.6 / ((670.501-561.455) / (2724-561.455))

[0068] =71.39t / h

[0069] 6. According to the calculated W 部进 =71.39t / h control the condensate flow rate entering the low-pressure steam flash tank.

[0070] The 1.44t / h of vented steam is no longer vented, and the heat is also recovered and utilized.

[0071] The above description is merely a typical embodiment of the present invention and does not impose any limitation on the present invention. Any changes or modifications made by those skilled in the art based on the above content without departing from the scope of the present invention should be considered equivalent examples of equivalent variations. Any equivalent changes made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are all within the scope of the present invention.

Claims

1. A process for eliminating steam venting, characterized in that: 1) The device produces high-grade condensate; 2) The high-grade condensate produced in step 1) is divided into two parts, one part of which is directly flashed into the low-pressure steam flash tank; the other part is directly sent out. 3) Step 2) The high-grade condensate entering the low-pressure steam flash tank is flashed to generate low-pressure flash steam and flashed low-pressure condensate; 4) After the low-pressure flash steam from step 3) enters the low-pressure steam network for use by the low-pressure heat exchanger, it generates low-pressure condensate, which is sent out together with or separately from the low-pressure condensate from step 3) flash steam.

2. The steam venting process according to claim 1, characterized in that: The device refers to a device that provides materials that require a heat source lower than that of low-pressure steam, and where the low-pressure steam produced by the low-pressure flash tank is in greater quantity than the demand for low-pressure steam from users.

3. The steam venting process according to claim 1, characterized in that: The high-grade condensate includes one or more types of high-pressure condensate, medium-pressure condensate, and low-pressure condensate.

4. The steam venting process according to claim 1, characterized in that: The high-grade condensate generated within the device is divided into two parts, each of which is one or more streams of low-pressure condensate.

5. The steam venting process according to claim 1, characterized in that: The high-grade condensate that directly enters the low-pressure steam flash tank must ensure that the amount of low-pressure steam flashed out in the low-pressure steam flash tank is equal to the amount of low-pressure steam required by the low-pressure steam heat exchanger.

6. The steam venting process according to claim 1, characterized in that: The flow rate of high-grade condensate directly entering the low-pressure steam flash tank is controlled by the pressure of the low-pressure steam network or the pressure of the low-pressure steam flash tank.

7. The steam venting process according to claim 1, characterized in that: The other portion of the high-grade condensate enters a condensate heat exchanger for heat exchange and is then discharged.

8. The steam venting process according to claim 7, characterized in that: The other portion of the high-grade condensate enters the condensate heat exchanger and then enters the low-pressure steam flash tank. The temperature after heat exchange is not higher than the saturation temperature corresponding to the flash pressure of the low-pressure steam flash tank.

9. The steam venting process according to claim 1, characterized in that: The condensate heat exchanger's cold source is one or more of cooling water, hot water, and lithium bromide, or one or more process materials whose heating temperature is lower than that of low-pressure condensate.

10. The steam venting process according to claim 1, characterized in that: A calculation module is set up in the device's DCS to perform feedforward control of the condensate flow rate entering the low-pressure flash tank. The calculation is performed according to the following steps: 1) Measure or calculate the low-pressure condensate flow rate W 进 ; 2) Based on the low-pressure condensate pressure and temperature, find the unit enthalpy H of the condensate from the steam property table. 进 ; 3) Measure or calculate the low-pressure steam demand W 出汽 4) Based on the operating pressure of the low-pressure steam flash tank, find the enthalpy value H of the steam at the operating pressure of the flash tank from the steam property table. 出汽 Enthalpy of condensate H 出水 ; 5) Calculate the required condensate volume W to enter the low-pressure flash tank using the following formula. 部进 , W 部进 =W 出汽 / ((H 进 -H 出水 ) / (H 出汽 -H 出水 )) 6) According to the calculated W 部进 Control the flow rate of condensate entering the low-pressure flash tank.

11. The steam venting process according to claim 1, characterized in that: The high-level condensate flow rate is controlled by a cascade control of the calculation module and the low-pressure steam network pressure or the low-pressure steam flash tank pressure.

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