A vacuum pumping system and method for multi-stage coupled condenser of coal-fired power station

Abstract

The present invention discloses a multi-stage coupled condenser vacuum pumping system and method for a coal-fired power plant, which comprises a condenser (1), two single-stage plain plate vacuum pump groups (2) with an output of 50%, two bipolar cone vacuum pump groups (3) with an output of 25%, a vacuum stop valve (4) and a pneumatic stop valve (5). When the condenser establishes a vacuum, both of the single-stage plain plate vacuum pump groups (2) are turned on to quickly establish a vacuum. When the condenser vacuum reaches the design value, only one bipolar cone vacuum pump group (3) is turned on to maintain the vacuum with low power consumption. It overcomes the disadvantages of the prior art that when the coal-fired power plant unit is started, the condenser needs to rely on a vacuum pump to quickly establish a vacuum; after reaching the design vacuum, only a small number of interfaces in the condenser have air leakage, and has the operating principle of using a single-stage pump to establish a vacuum and a two-stage cone pump to maintain a vacuum, and fully utilizes the advantages of the performance of different pump types in different ranges.

Description

Technical Field

[0001] The invention relates to the technical field of energy and chemical industry, and more specifically to a vacuum pumping system and method for a multi-stage coupled condenser of a coal-fired power station. Background Art

[0002] When the coal-fired power plant starts up, the condenser needs to rely on the vacuum pump to quickly establish a vacuum. When the vacuum pump establishes a vacuum, the pressure in the condenser gradually decreases from the atmospheric pressure of 101.3kPa to the design pressure of 5-10kPa. After reaching the design vacuum, only a small number of interfaces in the condenser have leakage. At this time, some vacuum pumps need to continue to work to maintain the vacuum in the condenser.

[0003] There are many types of vacuum pumps, and the two most commonly used in coal-fired power plants are single-stage plain disc vacuum pumps and bipolar cone vacuum pumps. The two pump bodies have their own advantages in establishing vacuum and maintaining vacuum. Figure 1 , Figure 2 These are the working performance curves of a single-stage pump and a bipolar cone pump of the same grade provided by a certain manufacturer.

[0004] like Figure 1 As shown ( Figure 1 The single-stage pump suction performance curve varies with the inlet pressure. In the working range of 101.3kPa to 5kPa, the peak suction volume of the single-stage pump can reach 3730m 3 / h, but when the inlet pressure drops from 10kPa to 5kPa, the air volume of the single-stage pump increases from 3620m 3 / h rapidly dropped to 3190m 3 / h, the suction capacity is reduced by about 11.8%.

[0005] like Figure 2 As shown ( Figure 2 The maximum suction capacity of the two-stage cone pump is 3510m 3 / h, less than 3730m3 of single-stage pump 3 / h, but when the inlet pressure drops from 10kPa to 5kPa, the air volume of the single-stage pump increases from 3550m 3 / h down to 3380m 3 / h, the suction capacity is only reduced by about 4.8%.

[0006] In summary, the single-stage pump has certain advantages in terms of pumping rate and total amount of air pumped, but the pumping performance of the single-stage pump decreases significantly in the low vacuum range (inlet pressure 5-10kPa), and the bipolar cone pump has certain performance advantages.

[0007] Coal-fired power plants require units to start quickly (i.e., condenser vacuum is established within 30 minutes), so single-stage pumps have large air extraction capacity and fast vacuum establishment, which is difficult to be replaced by other pump types. However, in the low vacuum range (inlet pressure 5-10kPa), the working efficiency decreases, the energy consumption increases, and even some projects have single-stage pumps with cavitation problems in this pressure range, which has caused serious safety accidents. Therefore, it is imperative to meet the two requirements of rapid vacuum establishment and low power consumption to maintain vacuum at the same time, and rationally design the vacuum system. Summary of the invention

[0008] The first object of the present invention is to overcome the deficiencies of the above-mentioned background technology and to provide a multi-stage coupled condenser vacuum pumping system for a coal-fired power plant.

[0009] The first objective of the present invention is implemented through the following technical scheme: a multi-stage coupled condenser vacuum pumping system for a coal-fired power plant, which includes a condenser, a single-stage plain disc vacuum pump group, a bipolar cone vacuum pump group, a vacuum stop valve and a pneumatic stop valve; two of the single-stage plain disc vacuum pump groups and two bipolar cone vacuum pump groups are arranged in parallel and connected to the condenser on one side through a mother pipe, and a vacuum stop valve and a pneumatic stop valve are provided on the branch pipe of each of the single-stage plain disc vacuum pump groups and the bipolar cone vacuum pump group, and each gas and water outlet of the condenser is provided with a vacuum stop valve.

[0010] In the above technical solution: the total output of two single-stage plain disc vacuum pump groups arranged in parallel is 100% of the system demand, each is 50%, and the total output of the two bipolar cone vacuum pump groups is 50% of the system demand, each is 25%.

[0011] The second object of the present invention is to provide a vacuuming method: a vacuuming method for a multi-stage coupled condenser of a coal-fired power plant, comprising the following steps;

[0012] ①. Open the vacuum stop valve at the condenser outlet, the vacuum stop valve and the pneumatic stop valve connected in series with the single-stage plain disc vacuum pump group, and keep all pipelines unobstructed.

[0013] ②. Start the two single-stage plain disc vacuum pump groups, and extract air from the condenser through the pipeline and start to build vacuum.

[0014] ③. When the condenser in step ② reaches the required vacuum degree, stop all the running single-stage plain disc vacuum pump groups, and close the vacuum stop valve and pneumatic stop valve connected in series with them; at the same time, open the vacuum stop valve and pneumatic stop valve connected in series with the bipolar cone vacuum pump group, and start one or two bipolar cone vacuum pump groups as needed; the total air extraction volume of the opened bipolar cone vacuum pump group should be greater than the air leakage volume of the condenser;

[0015] ④. Keep the bipolar cone vacuum pump group in step ③ running to keep the condenser in a vacuum state.

[0016] In the above technical solution: when one of the single-stage plain disc vacuum pump groups is damaged, two of the double-stage cone vacuum pump groups can be opened to replace it, so as to ensure the continuity and stability of the vacuum establishment process.

[0017] In the above technical solution: the number and capacity of the pump groups configured in the single-stage plain disc vacuum pump group plus the bipolar cone vacuum pump group in the steps ①-④ are sufficient to enable the single-stage plain disc vacuum pump group to establish vacuum and the bipolar cone vacuum pump group to maintain vacuum.

[0018] In the above technical solution: in step ①, the single-stage plain disc vacuum pump group needs to complete the vacuuming process of the condenser within 30 minutes.

[0019] The present invention has the following advantages:

[0020] 1. The two single-stage plain disc vacuum pump groups in the present invention are only used when the unit is started and the condenser establishes vacuum, and they can exert their advantages of large suction volume, fast suction speed and high energy efficiency in the normal pressure range.

[0021] 2. Under normal circumstances, the bipolar cone vacuum pump group in the present invention is only activated when maintaining vacuum. When operating in the low-pressure range, it can exert its advantages of high ultimate vacuum and high energy efficiency. In an emergency, when a single-stage pump fails, the two bipolar cone pumps in the present invention are turned on at the same time to replace the damaged single-stage pump.

[0022] 3. The single-stage plain disc vacuum pump group and the bipolar cone vacuum pump group in the present invention can be independently controlled by a vacuum stop valve and a pneumatic stop valve, and can be adjusted in time according to the operating conditions.

[0023] 4. The present invention uses two single-stage pumps with 50% output to establish vacuum, meeting the need for rapid vacuum establishment in the condenser, and at the same time uses a bipolar cone pump with 25% output to maintain the condenser vacuum, meeting the actual need for maintaining vacuum with low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The curve of the pumping performance of a single-stage pump provided by a manufacturer as a function of inlet pressure

[0025] Figure 2 The curve of the pumping performance of a two-stage pump provided by a manufacturer as a function of inlet pressure

[0026] Figure 3 It is a schematic diagram of the multi-stage coupled condenser vacuum pumping system of the present invention.

[0027] Figure 4 The schematic diagram of the existing single-stage plain disc vacuum pump condenser vacuum system is shown in FIG.

[0028] Figure 5 The schematic diagram of the existing bipolar cone vacuum pump condenser vacuum system is shown in FIG.

[0029] In the figure: condenser 1, single-stage plain disc vacuum pump group 2, bipolar cone vacuum pump group 3, vacuum stop valve 4, pneumatic stop valve 5, bipolar cone vacuum pump group 6. DETAILED DESCRIPTION

[0030] The implementation of the present invention will be described in detail below in conjunction with the accompanying drawings, but they do not constitute a limitation of the present invention and are only used as examples. At the same time, the advantages of the present invention will become clearer and easier to understand through the description.

[0031] Reference Figure 3 As shown: the present invention is a multi-stage coupled condenser vacuum pumping system for a coal-fired power plant, which includes a condenser 1, a single-stage plain disc vacuum pump group 2, a bipolar cone vacuum pump group 3, a vacuum stop valve 4, and a pneumatic stop valve 5; two of the single-stage plain disc vacuum pump groups 2 and two bipolar cone vacuum pump groups 3 are arranged in parallel and connected to the condenser 1 set on one side through a mother pipe, and a vacuum stop valve 4 and a pneumatic stop valve 5 are arranged on the pipeline of each of the single-stage plain disc vacuum pump group 2 and the bipolar cone vacuum pump group 3, and each gas and water outlet of the condenser 1 is provided with a vacuum stop valve 4.

[0032] The total output of the two parallel-arranged single-stage plain disc vacuum pump groups 2 is 100% of the system demand, each of which is 50%, and the total output of the two bipolar cone vacuum pump groups 3 is 50% of the system demand, each of which is 25%. The arrangement of the single-stage plain disc vacuum pump group 2 and the bipolar cone vacuum pump group 3 can make the total output of the system freely adjustable within the range of 25-150% and serve as a backup for each other, so that the system can cope with various changes in working conditions.

[0033] The present invention also includes a method for evacuating a condenser: a method for evacuating a multi-stage coupled condenser of a coal-fired power plant, comprising the following steps;

[0034] ①. Open the vacuum stop valve 4 at the outlet of the condenser, the vacuum stop valve 4 and the pneumatic stop valve 5 connected in series with the single-stage plain disc vacuum pump group 2, and keep all pipelines unobstructed.

[0035] ②. Start both of the single-stage plain disc vacuum pump groups 2 to extract air from the condenser 1 through the pipeline and start to establish vacuum.

[0036] ③. When the condenser 1 in step ② reaches the required vacuum degree, stop all single-stage plain disc vacuum pump groups 2, and close the vacuum stop valve 4 and pneumatic stop valve 5 connected in series with them. At the same time, open the vacuum stop valve 4 and pneumatic stop valve 5 connected in series with the bipolar cone vacuum pump group 3, and start 1-two bipolar cone vacuum pump groups 3. The total suction volume of the bipolar cone vacuum pump group 3 that is turned on should be greater than the leakage volume of the condenser 1;

[0037] ④. Keep the bipolar cone vacuum pump group 3 in step ③ running to keep the condenser 1 in a vacuum state.

[0038] When one of the single-stage plain disc vacuum pump groups 2 is damaged, two of the double-stage cone vacuum pump groups 3 can be opened to replace it, thereby ensuring the continuity and stability of the vacuum establishment process.

[0039] The configuration is not limited to two single-stage plain disc vacuum pump groups 2 + two bipolar cone vacuum pump groups 3. The number and capacity of the pump groups can be flexibly configured according to the actual project. In the step ①, the principle of single-stage plain disc vacuum pump group 2 establishing vacuum and bipolar cone vacuum pump group 3 maintaining vacuum is sufficient. This principle can simultaneously ensure rapid establishment of vacuum and low power consumption to maintain vacuum, thereby greatly reducing system energy consumption.

[0040] In steps ①-④, the single-stage plain disc vacuum pump group 2 needs to complete the vacuuming process of the condenser 1 within 30 minutes.

[0041] Reference Figure 4 As shown: In the prior art, the condenser vacuum system is usually equipped with three single-stage plain plate vacuum pump groups 2 with 50% output. That is, two single-stage plain plate vacuum pump groups 2 are in normal use, and one single-stage plain plate vacuum pump group 2 is in standby. When the condenser 1 vacuum is established, the two pump groups are turned on at the same time, and one is stopped to reduce power consumption when the vacuum is maintained. The above-mentioned 2-in-1-standby configuration method is mature in technology, stable in operation, has a large air extraction capacity, can quickly establish a vacuum, and is widely used.

[0042] However, the single-stage plain disc vacuum pump group 2 has high power consumption and low efficiency under low pressure conditions, and its single 50% output is far greater than the condenser's vacuum requirement. Therefore, this configuration has high energy consumption, low efficiency, and poor economy during operation. It is also difficult to ensure the condenser vacuum under low pressure conditions, which is not conducive to promotion and use.

[0043] Reference Figure 5As shown: in the prior art; in order to solve the problem of low efficiency under low vacuum conditions, some projects use a 50% output bipolar cone vacuum pump group 6 to replace the single-stage plain disc vacuum pump group 2. When establishing the vacuum of the condenser 1, two or three bipolar cone vacuum pump groups 6 are turned on at the same time, and only one pump group is operated to maintain the vacuum to reduce power consumption. Since the bipolar cone vacuum pump group 6 has a high exhaust efficiency under low vacuum conditions, it can better solve the vacuum problem during operation.

[0044] However, since the pump group selection must meet the requirement of establishing condenser vacuum within 30 minutes, the bipolar cone vacuum pump group 6 model is often larger, and the problems of high power consumption and poor economy have not been completely solved; therefore, it is not suitable for promotion and use.

[0045] Reference Figure 3 As shown: The present invention provides a specific embodiment: first, when the coal-fired power plant unit is started, two single-stage plain disc vacuum pump groups 2 with 50% output are turned on at the same time to quickly establish the vacuum of the condenser 1.

[0046] After the vacuum is established in the condenser 1 , the two single-stage plain disc vacuum pump groups 2 are turned off, and at the same time, a single-stage bipolar cone vacuum pump group 3 with a 25% output is turned on to maintain the vacuum state of the condenser 1 .

[0047] All pump groups of the present invention are designed in parallel and are independently controlled by vacuum stop valve 4 and pneumatic stop valve 5. When the condenser 1 establishes vacuum, if one of the single-stage plain disc vacuum pump groups 2 with 50% output fails, two single-stage bipolar cone vacuum pump groups 3 with 25% output can replace it. When the condenser 1 maintains vacuum, if one of the single-stage bipolar cone vacuum pump groups 3 with 25% output fails, another single-stage bipolar cone vacuum pump group 3 can replace it.

[0048] The bipolar cone vacuum pump group 3 can be equipped with a bipolar cone vacuum pump group 3 with a frequency conversion device according to the working conditions to further reduce the operating power consumption. The single-stage plain plate vacuum pump group 2 and the bipolar cone vacuum pump group 3 in the present invention can be replaced with their vacuum pump forms when necessary, and the large-capacity pump body only needs to quickly establish vacuum and the small-capacity pump body maintains the vacuum of the condenser 1.

[0049] Example 2: Taking a 600MW unit in a power plant in my country as an example, the investment and operating costs of the present invention and the conventional system are compared and calculated.

[0050] The designed extraction gas volume of the power plant's condenser is 61.23kg / h, the annual utilization hours are 7000h, the standard coal price is 1400 yuan / ton, and the unit heat consumption is 7977kJ / kWh.

[0051] Solution 1: Conventional configuration: 3 single-stage pumps with 50% capacity (2 for use and 1 for backup, e.g. Figure 4 As shown), Option 2: Configure 3 50% capacity bipolar cone vacuum pumps (2 for use and 1 for backup, as shown Figure 3 As shown), Scheme 3: Referring to the present invention, configure two 50% output single-stage plain disc vacuum pump groups 2 + two 25% output bipolar cone vacuum pump groups 3 (as shown Figure 1 shown).

[0052] The calculation method is as follows:

[0053] 1) Annual fixed fee

[0054] The cost of the system is calculated using the annual cost method:

[0055] AC=P(FCR)

[0056]

[0057] Where:

[0058] AC: Annual fixed cost n: Economic operation period, 15 years

[0059] P: Total system investment, RMB 900,000 to RMB 1,350,000 i: Benchmark rate of return, 8%

[0060] FCR: Annual fixed charge rate

[0061] 2) Annual operating costs

[0062] The running cost is calculated as follows:

[0063] OM1=(PhH R / ηS C ) c

[0064] P=UI

[0065] Where:

[0066] OM1: Annual operating cost η: Boiler efficiency, 0.943

[0067] P: Actual power consumption H R :Unit heat consumption, 7977kJ / kWh

[0068] h: annual utilization hours, value is 7000 P c : Standard coal price, 1400 yuan / ton

[0069] U: Rated voltage, 380V S c : Standard coal calorific value, 29301kJ / kg

[0070] I: operating current, 90-230A

[0071] 3) Annual maintenance costs

[0072] Annual maintenance cost = initial investment cost × 2.5%

[0073] 4) Annual Fees

[0074] Annual cost = annual fixed cost + annual operating cost + annual inspection and maintenance cost

[0075] unit Solution 1 Solution 2 Option 3 Initial investment Ten thousand yuan 90 135 90 Benchmark yield ％ 0.08 0.08 0.08 Economic operation period Year 15 15 15 Annual fixed fee rate \ 0.117 0.117 0.117 Annual fixed fee Ten thousand yuan 10.51 15.77 10.51 Operating current A 230 170 90 Annual utilization hours h 7000 7000 7000 Unit heat consumption kJ / kWh 7977 7977 7977 Standard coal price Yuan / ton 1400 1400 1400 Standard coal calorific value kJ / kg 29301 29301 29301 Operating costs Ten thousand yuan 24.73 18.28 9.68 Repair and maintenance costs Ten thousand yuan 2.25 3.375 2.25 Annual Cost Ten thousand yuan 37.49 31.14 24.76 Annual cost difference Ten thousand yuan Benchmarks -6.345 -12.728

[0076] The above calculation results show that the multi-stage coupled condenser vacuum pumping system (Scheme 3) disclosed in the present invention has the lowest operating cost and the lowest annual cost under the same boundary conditions.

[0077] The parts not described in detail above are all prior art.

Claims

1. A method for vacuuming a multi-stage coupled condenser in a coal-fired power plant using a multi-stage coupled condenser vacuum pumping system in a coal-fired power plant, the multi-stage coupled condenser vacuum pumping system in a coal-fired power plant comprising a condenser (1), a single-stage plain disc vacuum pump group (2), a bipolar cone vacuum pump group (3), a vacuum stop valve (4) and a pneumatic stop valve (5); two of the single-stage plain disc vacuum pump groups (2) and two bipolar cone vacuum pump groups (3) are arranged in parallel and connected to the condenser (1) on one side through a mother pipe, a vacuum stop valve (4) and a pneumatic stop valve (5) are provided on the branch pipe of each of the single-stage plain disc vacuum pump group (2) and the bipolar cone vacuum pump group (3), and each gas-water outlet of the condenser (1) is provided with a vacuum stop valve (4); characterized in that: The method comprises the following steps: ①. Open the vacuum stop valve (4) provided at the outlet of the condenser (1), the vacuum stop valve (4) and the pneumatic stop valve (5) connected in series with the single-stage plain disc vacuum pump unit (2), and keep all pipelines unobstructed; ②, starting the two single-stage plain disc vacuum pump groups (2), and extracting air from the condenser (1) through the pipeline to start building a vacuum; ③. When the condenser (1) in step ② reaches the required vacuum degree, all the running single-stage plain disc vacuum pump groups (2) are stopped, and the vacuum stop valve (4) and the pneumatic stop valve (5) connected in series with the same are closed; at the same time, the vacuum stop valve (4) and the pneumatic stop valve (5) connected in series with the bipolar cone vacuum pump group (3) are opened, and one or two bipolar cone vacuum pump groups (3) are started as needed; the total air extraction volume of the opened bipolar cone vacuum pump group (3) should be greater than the air leakage volume of the condenser (1); ④. Keep the bipolar cone vacuum pump group (3) in step ③ running, so that the condenser (1) is continuously kept in a vacuum state.

2. A method for vacuuming a multi-stage coupled condenser in a coal-fired power plant using a vacuuming system for a multi-stage coupled condenser in a coal-fired power plant according to claim 1, characterized in that: The total output of the two parallel-arranged single-stage plain disc vacuum pump groups (2) is 100% of the system demand, with each group accounting for 50%. The total output of the two bipolar cone vacuum pump groups (3) is 50% of the system demand, with each group accounting for 25%.

3. A method for vacuuming a multi-stage coupled condenser in a coal-fired power plant using a vacuuming system for a multi-stage coupled condenser in a coal-fired power plant according to claim 1, characterized in that: When one of the single-stage plain disc vacuum pump groups (2) is damaged, two of the double-stage cone vacuum pump groups (3) can be opened to replace it, so as to ensure the continuity and stability of the vacuum establishment process.

4. A method for vacuuming a multi-stage coupled condenser in a coal-fired power plant using a vacuuming system for a multi-stage coupled condenser in a coal-fired power plant according to claim 1, characterized in that: The number and capacity of the pump groups configured by the single-stage plain disc vacuum pump group (2) plus the bipolar cone vacuum pump group (3) are sufficient to enable the single-stage plain disc vacuum pump group (2) to establish a vacuum and the bipolar cone vacuum pump group (3) to maintain a vacuum in the steps ① to ④.

5. The method for evacuating a multi-stage coupled condenser in a coal-fired power plant by using a multi-stage coupled condenser evacuation system in a coal-fired power plant according to claim 1, characterized in that: In step ①, the single-stage plain disc vacuum pump group (2) needs to complete the vacuuming process of the condenser (1) within 30 minutes.

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