Method for preventing water accumulation caused by flow loss in a steam-water heat exchanger

Abstract

The application discloses a method for preventing water accumulation caused by steam-water heat exchanger flow loss, and the features include: through load calculation, a well-configured temperature control system is configured to ensure the pressure difference before and after the main drain valve, so that the generated condensate is discharged from the steam-water heat exchanger in time, the installation position of the main drain valve group is lowered, a flow loss prevention branch is led out between the steam-water heat exchanger and the main drain valve group, an auxiliary drain valve is arranged in the flow loss prevention branch and directly discharged to the waste water pipeline; a small-resistance drain valve is selected, and the type and diameter of the drain valve are determined according to the system pressure, pressure difference and condensate amount. The method improves the equipment utilization, heat exchange efficiency and system reliability, adjusts the position difference between the steam-water heat exchanger outlet and the auxiliary drain valve, facilitates the connection with the waste water pipeline nearby, effectively ensures that the steam-water heat exchanger does not lose flow, and makes the equipment truly reach the design life.

Description

Technical Field

[0001] This invention relates to heat exchange engineering technology, and in particular to a method for preventing water accumulation in steam-water heat exchangers due to flow loss. Background Technology

[0002] In industrial production, centralized steam heating is widely used because, from a heat transfer perspective, phase change heat transfer has a higher heat transfer coefficient than single-phase heat transfer. The heat transfer coefficient utilizing steam condensation can reach as high as 2500–15000 W / (m³). 2 In applications where steam cannot be used directly, hot water at various temperatures is often required as a heat source. For example, 95°C hot water is ideal for heating. This necessitates the use of a steam-water heat exchanger, which transfers the heat from the steam to the hot water used for heating. Therefore, steam-water heat exchangers have a wide range of applications.

[0003] The pressure of the condensate at the outlet of the steam trap is called the back pressure of the steam trap. It is used to overcome the resistance of the condensate pipeline and to raise the condensate to a certain height. When the steam-water heat exchanger is under low load and the back pressure of the steam trap is high, the automatic temperature control valve opens too low, resulting in insufficient pressure or even a vacuum state inside the heat exchanger. The condensate cannot flow back to the condensate recovery pipeline, and water accumulates inside the heat exchanger. This situation is called loss of flow.

[0004] High back pressure in the steam trap and low steam pressure in the heat exchanger mean that either situation will result in insufficient pressure differential to discharge condensate from the heat exchanger through the steam trap to the condensate recovery pipe. This inability to discharge condensate leads to water accumulation in the heat exchanger.

[0005] When designing a heating system, the outdoor calculated temperature for winter heating load is based on the average daily temperature over a period of several years, without a guaranteed 5-day period. In actual operation, the air temperature is higher than this for most of the time, resulting in a heating load lower than the designed full load, which varies with the seasons. This lower load leads to a decrease in heat exchanger steam pressure, potentially causing flow loss. Due to variable climatic conditions, this flow loss phenomenon is characterized by its persistence and irregularity.

[0006] The specific mechanism is as follows:

[0007] 1. During the temperature control cycle, when the water temperature rises, the opening of the steam control valve decreases, the steam pressure decreases, and the pressure of the condensate at the inlet of the steam trap decreases.

[0008] 2. When the steam pressure drops, the inlet pressure of the steam trap becomes lower than the condensate pressure at the outlet. Condensate in the steam-water heat exchanger cannot be discharged, resulting in water accumulation and a loss of flow. Simply put, the steam pressure is insufficient to force condensate through the steam trap. After this loss of flow occurs, water accumulates in the steam-water heat exchanger, the water temperature drops, and the steam flow rate through the temperature control valve increases.

[0009] 3. When the steam pressure rises, the pressure of the condensate at the inlet of the steam trap is greater than the pressure of the condensate at the outlet. The steam-water heat exchanger begins to discharge condensate. When the high-temperature steam encounters the low-temperature condensate, the steam loses heat and transforms into condensate, which is 1000 times smaller in volume than the steam. During the condensation process, the reduced volume of the steam temporarily creates a vacuum, and the condensate is drawn into this vacuum space. The condensate surges and collides within the equipment, forming water hammer. This phenomenon is prone to occur and continuously circulates.

[0010] Loss of flow leads to water accumulation in the steam-water heat exchanger, which has many adverse effects, including the following:

[0011] Oxygen and carbon dioxide in steam dissolve more readily in condensate, exacerbating heat exchanger corrosion. Temperature differences between the upper and lower parts of a steam-water heat exchanger can cause mechanical stress, particularly damaging welded heat exchangers. Water hammer can easily damage the heat exchanger. When a steam-water heat exchanger heats air, the bottom coil is prone to freezing and cracking in winter. Control valve oscillations accelerate equipment wear. Increased temperature fluctuations on the user side of the steam-water heat exchanger significantly impact heating quality and comfort. Equipment lifespan is severely reduced; for example, heat exchangers, control valves, and other equipment and components originally designed for a 15-year lifespan may need to be replaced within 2-3 years due to flow loss issues. This increases replacement costs and additional labor costs, and if the replaced equipment serves production processes, it can lead to significant downtime and production losses due to equipment maintenance. Summary of the Invention

[0012] The purpose of this invention is to solve the problem of flow loss during the operation of traditional steam-water heat exchangers and to provide a method to prevent water accumulation caused by flow loss in steam-water heat exchangers. Based on the actual situation of specific projects, it sets up an adjustable auxiliary drainage device and proposes a calculation and selection method for the auxiliary drainage device. It has the characteristics of strong operability, improving equipment heat exchange efficiency and equipment utilization, and ensuring system reliability.

[0013] The above-mentioned technical problem of the present invention is mainly solved by the following technical solution: a method for preventing water accumulation due to loss of flow in a steam-water heat exchanger, characterized by the following:

[0014] (i) By calculating the load and configuring a good temperature control system, the pressure difference before and after the main drain valve is ensured so that the generated condensate is discharged from the steam-water heat exchanger in a timely manner.

[0015] Calculation of loss-of-flow condition for steam-water heat exchanger:

[0016] a. Determine the heat exchange area based on the heat source temperature, user-end heat load, inlet and outlet water temperatures, and the heat transfer coefficient of the heat exchanger sample.

[0017] b. Based on the selected steam-water heat exchanger area, calculate the design operating conditions of the steam temperature, pressure, and steam flow rate of the steam-water heat exchanger (1).

[0018] c. Calculate the heat exchanger operating pressure and temperature corresponding to the condensate stagnation and accumulation before the main drain valve by using the back pressure after the main drain valve, and then determine the loss-flow condition.

[0019] d. Calculate the heat load rate of the steam-water heat exchanger under off-flow conditions:

[0020] 1) Introduce the temperature design constant (TDC) to determine the operating temperature inside the steam-water heat exchanger under any load, assuming a constant secondary fluid flow rate:

[0021]

[0022] Where: TDC: Temperature design constant (dimensionless), T s T1: Saturated steam temperature inside the steam-water heat exchanger (°C), T2: Secondary fluid inlet temperature (°C), T3: Secondary fluid outlet temperature (°C).

[0023] The inlet and outlet temperatures of the secondary fluid are obtained from Formula 1.

[0024] 2) Calculate the heat exchange power using formula 2:

[0025] O=CpmΔT Formula 2

[0026] Where: Q: heat exchange power (kW), m: mass flow rate (kg / s); C P : Specific heat at constant pressure (kJ / (kg℃)); ΔT: Temperature difference between the inlet and outlet water on the secondary side of the heat exchanger (℃).

[0027] The heat exchange power of the steam-water heat exchanger can be obtained from Formula 2, and then the heat load rate can be obtained.

[0028] (ii) Lower the installation position of the main drain valve group, and lead out a branch line (5) to prevent flow loss at point C between the steam-water heat exchanger and the main drain valve group. Install an auxiliary drain valve in the branch line to directly discharge to the wastewater pipeline.

[0029] (iii) Select a steam trap with low resistance. Determine the model and diameter of the steam trap based on the system pressure, pressure difference and condensate volume.

[0030] In the aforementioned method for preventing water accumulation due to flow loss in steam-water heat exchangers, preferably, in part (a), when determining the heat exchange area, the minimum heat exchange area required to meet the heat exchange requirements under the highest load is first determined by using the logarithmic mean temperature difference ΔTm of the steam-water heat exchanger.

[0031] The logarithmic mean temperature difference ΔTm:

[0032]

[0033] Where: ΔT m Ts: Logarithmic mean temperature difference (°C); T1: Saturated steam temperature (°C); T2: Secondary side inlet water temperature (°C); Ln: Natural logarithm (dimensionless);

[0034] The minimum required heat exchange area is:

[0035]

[0036] Where: A: heating area (m²) 2 Q: Heat transfer power (W); U: Heat transfer coefficient (W / (m²)); 2 ·℃); ΔTm: logarithmic mean temperature difference (℃).

[0037] In the aforementioned method for preventing water accumulation due to loss of flow in the steam-water heat exchanger, as a preferred embodiment, in content (ii), the height difference h1 between the anti-loss-flow branch at point C and the main drain valve is ≥300mm.

[0038] In the aforementioned method for preventing water accumulation due to loss of flow in the steam-water heat exchanger, as a preferred embodiment, in content (ii), when the anti-loss-flow branch is led out from point C, adjustable-length telescopic corrugated pipes (6) are respectively installed in the upper and lower sections in the height direction of point C.

[0039] In the aforementioned method for preventing water accumulation due to loss of flow in the steam-water heat exchanger, preferably, in content (ii), the location of point C is ≤1m below the heat exchanger outlet.

[0040] In the aforementioned methods for preventing water accumulation due to loss of flow in steam-water heat exchangers, as a preferred option, in content (iii), the selection of the steam trap should meet the drainage requirements under low pressure differential conditions.

[0041] In the aforementioned method for preventing water accumulation due to loss of flow in the steam-water heat exchanger, preferably, when selecting the heat exchange area of ​​the steam-water heat exchanger, the determined heat exchange area is ≥ (1+5%) the minimum heat exchange area.

[0042] In the aforementioned method for preventing water accumulation due to loss of flow in the steam-water heat exchanger, preferably, a plunger valve (501) is provided at the inlet end of the auxiliary steam trap (502) in the branch line leading out from point C to prevent loss of flow.

[0043] In the aforementioned method for preventing water accumulation due to loss of flow in the steam-water heat exchanger, preferably, the main drain valve and the auxiliary drain valve are selected using the same method.

[0044] This technical solution starts from the original working principle of the steam-water heat exchanger, conducts a comprehensive and systematic analysis of the causes of flow loss during its operation, verifies the correlation of each flow loss factor, finds the flow loss critical point through calculation, and rationally configures each control element; and introduces an anti-flow loss branch as an auxiliary drainage pipeline, so that once condensate occurs in the heat exchanger, multiple drainage protection pipelines ensure that the condensate is discharged in a timely and smooth manner, thus solving the problem of condensate retention at its root.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] 1. It increases the load range of the steam-water heat exchanger without loss of flow, thus improving equipment utilization.

[0047] 2. Without increasing energy consumption, the heat exchange equipment is guaranteed to maintain flow and heat exchange efficiency is improved.

[0048] 3. In the event of a failure in the main drainage pipeline, the auxiliary drainage pipeline can be used to replace the drainage, thereby improving system reliability.

[0049] 4. It is adjustable, and by adjusting the height difference between the outlet of the steam-water heat exchanger and the auxiliary drain valve, it is convenient to connect to nearby wastewater pipelines.

[0050] 5. Through accurate calculations and scientific guidance, and by operating and managing the equipment in accordance with regulations, it is possible to effectively ensure that the steam-water heat exchanger does not lose flow, thus enabling the equipment to truly reach its design life. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of one embodiment of the present invention.

[0052] Figure 2 yes Figure 1 Schematic diagram of the anti-loss branch in the circuit.

[0053] In the diagram: 1. Steam-water heat exchanger, 2. Condensate recovery main line, 3. Condensate recovery manifold, 4. Saturated steam input line, 5. Anti-loss branch line, 501. Piston valve, 502. Auxiliary steam trap, 6. Expansion bellows.

[0054] h. The height to which the condensate pipe of the steam-water heat exchanger is raised after passing through the main drain valve. Detailed Implementation

[0055] The technical solution of the present invention will be further described in detail below through embodiments and with reference to the accompanying drawings. This embodiment provides a method for preventing water accumulation in a steam-water heat exchanger due to flow loss, comprising the following:

[0056] (i) By calculating the load and configuring a good temperature control system, the pressure difference before and after the main drain valve is ensured so that the generated condensate is discharged from the steam-water heat exchanger in a timely manner.

[0057] Calculation of loss-of-flow condition for steam-water heat exchanger:

[0058] a. Determine the heat exchange area based on the heat source temperature, user-end heat load, inlet and outlet water temperatures, and the heat transfer coefficient of the heat exchanger sample.

[0059] When determining the heat exchange area, the minimum heat exchange area required to meet the heat exchange requirements under the highest load is first determined by the logarithmic mean temperature difference ΔTm of the steam-water heat exchanger.

[0060] The logarithmic mean temperature difference ΔTm:

[0061]

[0062] Where: ΔTm: logarithmic mean temperature difference (°C); Ts: saturated steam temperature (°C); T1: secondary side inlet water temperature (°C); T2: secondary side outlet water temperature (°C); Ln: natural logarithm (dimensionless).

[0063] The minimum required heat exchange area is:

[0064]

[0065] Where: A = heating area (m²) 2 Q = heat transfer power (W); U = heat transfer coefficient (W / (m²)) 2 ·℃); ΔTm: logarithmic mean temperature difference (℃).

[0066] b. Based on the selected steam-water heat exchanger area, calculate the steam temperature, pressure, and steam flow rate inside steam-water heat exchanger 1. When selecting the heat exchange area of ​​the steam-water heat exchanger, the determined heat exchange area should be ≥ (1 + 5%) of the minimum heat exchange area.

[0067] c. Calculate the heat exchanger operating pressure and temperature corresponding to the condensate stagnation and accumulation before the main drain valve by using the back pressure after the main drain valve, and then determine the loss-flow condition.

[0068] d. Calculate the heat load rate of the steam-water heat exchanger under off-flow conditions:

[0069] 1) Introduce the temperature design constant (TDC) to determine the operating temperature inside the steam-water heat exchanger under any load, assuming a constant secondary fluid flow rate:

[0070]

[0071] Where: TDC: Temperature design constant (dimensionless), T s T1: Saturated steam temperature inside the steam-water heat exchanger (°C), T2: Secondary fluid inlet temperature (°C), T3: Secondary fluid outlet temperature (°C).

[0072] The inlet and outlet temperatures of the secondary fluid are obtained from Formula 1.

[0073] Calculate the heat exchange power using Formula 2:

[0074] Q=CpmΔT Formula 2

[0075] Where: Q: heat exchange power (kW), m: mass flow rate (kg / s); C P : Specific heat at constant pressure (kJ / (kg℃)); ΔT: Temperature difference between the inlet and outlet water on the secondary side of the heat exchanger (℃).

[0076] The heat exchange power of the steam-water heat exchanger can be obtained from Formula 2, and then the heat load rate can be obtained.

[0077] (ii) Lower the installation position of the main drain valve assembly, and extend a branch line 5 for preventing flow loss from point C between the steam-water heat exchanger and the main drain valve assembly, directly discharging into the wastewater pipeline, such as... Figure 1 , Figure 2 As shown, an auxiliary drain valve 502 is installed in the anti-loss branch 5, and a plunger valve 501 is provided at the inlet end of the auxiliary drain valve 502.

[0078] The height difference h1 between the anti-loss branch at point C and the main drain valve is ≥300mm; the position of point C is ≤1m below the heat exchanger outlet.

[0079] When the anti-loss branch is drawn from point C, adjustable-length telescopic corrugated pipes 6 are installed at the upper and lower sections in the height direction of point C.

[0080] (III) Select steam traps with low resistance. Determine the model and diameter of the steam trap based on the system pressure, pressure difference, and condensate flow. When selecting steam traps, ensure they meet drainage requirements under low pressure difference conditions. Note: The selection method for main steam traps and auxiliary steam traps is the same.

[0081] The following example uses a specific engineering project as an illustration:

[0082] A factory needs to install a steam-water heat exchanger 1. The installation system of steam-water heat exchanger 1 is as follows: Figure 1As shown, the pressures at both ends of the control valve in the saturated steam input pipeline 4 are P0 at the front and P1 at the rear (i.e., the steam side inside the steam-water heat exchanger). The functional components of the condensate recovery main pipeline 2, following the steam flow direction, are a plunger valve, a main drain valve, a plunger valve, and a check valve. The functional components of the anti-loss-flow branch pipeline 5 are a plunger valve and an auxiliary drain valve. The steam pressure of the heat source is 0.5 MPa (absolute pressure, the rest are the same), heating water from 70℃ to 95℃. Figure 1 The hot water flow direction of the steam-water heat exchanger 1 is bottom inlet and top outlet, the circulating water flow rate is 2.8 kg / s, and the designed heat exchange power is 293.3 kW. The condensate column height is adjusted by the telescopic corrugated pipe 6.

[0083] After passing through the main steam trap, the condensate pipe from the steam-water heat exchanger 1 is lifted 6m (h in the diagram) into the condensate recovery pipe 3. Considering the frictional resistance along the pipe and the local frictional resistance of the valves, the back pressure after the main steam trap is 0.2MPa. The appropriate type and diameter of steam trap must be selected based on the system's operating conditions to ensure effective condensate removal from the steam-water heat exchanger 1 under any circumstances.

[0084] (i) By calculating the load and configuring a good temperature control system, the pressure difference before and after the main drain valve is ensured so that the generated condensate is discharged from the steam-water heat exchanger in a timely manner.

[0085] Calculation of loss-of-flow condition for steam-water heat exchanger:

[0086] a. Design calculations

[0087] The heat load under design conditions is determined from heat balance formula 2, which gives the design heat load as follows:

[0088] Heat exchange power Q = 4.19 × 2.8 × (95 - 70) = 293.3 KW.

[0089] The minimum heat exchange area required to meet the heat exchange requirements under the highest load; before that, it is necessary to first determine the logarithmic mean temperature difference ΔTm of the steam-water heat exchanger.

[0090] From Formula 3:

[0091]

[0092] Where: Ts = 151.8 (°C), corresponding to the saturated steam temperature at 0.5 MPa pressure; T1 = 70 (°C), secondary side inlet water temperature; T2 = 95 (°C), secondary side outlet water temperature. Substituting these values ​​into the equation:

[0093]

[0094] Therefore: ΔTm = 68.54℃

[0095] The heat exchange power at the highest load is 293.3kW. The minimum required heat exchange area can then be calculated using Formula 4.

[0096]

[0097] Select a plate heat exchanger with a heat exchange area of ​​1.7973 m² from the product model list in the heat exchanger catalog. This heat exchanger is slightly larger than expected (5% larger), therefore, the actual working pressure of the steam space will be lower than 0.5 MPa when operating at full load.

[0098] b. Verification calculation:

[0099] Based on the selected heat exchanger area, the steam temperature, pressure, and steam flow rate inside steam-water heat exchanger 1 were calculated, and the heat exchange area was determined to be 1.7973 m². 2 The logarithmic mean temperature difference of the heat exchanger.

[0100] From Formula 4 Transform and substitute the data:

[0101]

[0102] The result is ΔTm = 65.28℃.

[0103] Simultaneously, the steam temperature inside the heat exchanger under full load can be obtained by transforming Equation 3:

[0104]

[0105] Solving the logarithmic equation, we get Ts = 148.6℃.

[0106] The saturated steam pressure at this temperature is 0.46 MPa. Since this pressure is greater than the back pressure of the main steam trap (0.2 MPa), the system will not experience flow loss at full load.

[0107] Determine the steam flow rate at full load:

[0108] The mass flow rate of steam depends on the pressure of the steam space. At full load, the pressure of the steam space is 0.46 MPa. According to Table 1-31 of the Power Piping Design Manual, 2nd Edition, the latent heat of saturated steam is 2117.2 KJ / kg.

[0109] Obtained from the following formula:

[0110]

[0111]

[0112] Steam flow rate = 498.7 kg / h (at full load).

[0113] c. Analysis of loss of current operating conditions:

[0114] When the heat load decreases, the steam temperature in the steam-water heat exchanger decreases, and the saturation pressure decreases accordingly. When it decreases to a certain level, the pressure at the inlet of the steam trap is less than the pressure of the condensate at the outlet of the steam trap. The condensate cannot be discharged through the main steam trap. At this time, the check valve at the outlet of the main steam trap prevents the condensate from flowing back. As a result, the condensate stagnates between the steam-water heat exchanger and the main steam trap. When the pressure inside the heat exchanger plus the sum of the static pressure head of the water column between the outlet of the heat exchanger and the main steam trap is still insufficient to overcome the pressure of the condensate at the outlet of the main steam trap, i.e., the back pressure at the outlet of the main steam trap is 0.2 MPa, the condensate will flow back into the steam-water heat exchanger, causing water accumulation and resulting in a loss of flow.

[0115] d. Calculate the heat load rate of the steam-water heat exchanger under off-flow conditions.

[0116] Introducing the temperature design constant (TDC), the operating temperature within a steam-water heat exchanger under any load is determined with a constant secondary fluid flow rate. Since the logarithmic mean temperature difference method is typically used to select heat exchangers during design, once the heat exchanger is selected, for any heat exchanger using steam as the heating medium, the TDC method can be used to determine the operating temperature within the heat exchanger under any load, provided the secondary fluid flow rate remains unchanged.

[0117] The temperature design constant refers to the ratio of the steam temperature to the temperature difference between the inlet and outlet of the secondary fluid, as shown in Formula 1:

[0118]

[0119] In the formula: steam pressure = 0.46 MPa, inlet water temperature T1 = 70℃, outlet water temperature T2 = 95℃, and saturated steam temperature Ts = 148.6℃ at 0.46 MPa.

[0120] Then TDC = 1.4664

[0121] When the heat exchanger is close to the loss-of-flow condition, the saturated steam pressure is approximately equal to the back pressure of the steam trap, which is 0.2 MPa. The saturated steam temperature corresponding to 0.2 MPa is 120.23℃.

[0122] The secondary inlet water temperature can be obtained from the following formula:

[0123] T1 = Ts - TDC × (Ts - T2)

[0124] In the formula: T1 is the secondary side inlet water temperature, T2 is the secondary side outlet water temperature (95℃), Ts = 120.23℃, and TDC = 1.4664.

[0125] Then T1 = 120.23 - [1.4664 × (120.23 - 95)] = 83.2℃.

[0126] Then calculate the heat exchange power using Formula 2:

[0127] Q=2.8×4.19×(95-83.2)=138.4kW

[0128] The load factor is: 138.4 / 293.3 × 100% = 47.2%.

[0129] That is, when the heat load reaches 47.2%, the condensate in front of the main steam trap begins to stagnate. As the load continues to decrease, when the pressure inside the heat exchanger plus the sum of the static pressure head of the water column between the heat exchanger outlet and the main steam trap is still unable to overcome the pressure of the condensate at the outlet of the main steam trap, i.e., the back pressure at the outlet of the main steam trap is 0.2 MPa, the condensate will flow back into the steam-water heat exchanger, causing a loss of flow.

[0130] (ii) Lower the installation position of the main drain valve assembly, and lead out the anti-loss branch 5 at point C between the steam-water heat exchanger and the main drain valve assembly. Install an auxiliary drain valve in the anti-loss branch 5 and discharge it directly to the wastewater pipeline.

[0131] During normal operation, due to the density difference between condensate and steam, condensate flows directly to the main steam trap of the condensate recovery main line and does not flow through the anti-flow branch 5. When the heat load continues to drop below approximately 47.2%, the main steam trap cannot properly discharge condensate, and condensate begins to stagnate in the pipe section before the main steam trap. When the condensate column reaches point C, it will flow through the branch pipe to the anti-flow branch 5. As long as the pressure inside the steam-water heat exchanger 1 remains greater than atmospheric pressure by 0.1 MPa, the condensate will be smoothly discharged through the anti-flow branch 5. When the load continues to decrease and the pressure inside the steam-water heat exchanger 1 is less than atmospheric pressure by 0.1 MPa, the condensate will stagnate in the pipe section before the auxiliary steam trap in the anti-flow branch 5. When the pressure inside the heat exchanger plus the sum of the static pressure head of the water column between the heat exchanger outlet and the anti-flow branch is still less than atmospheric pressure, flow loss will be inevitable. This is the critical point for flow loss in the steam-water heat exchanger 1.

[0132] According to the information obtained, the saturated steam temperature at 0.1 MPa pressure is approximately 100℃. This is the temperature at which the steam-water heat exchanger 1 reaches the loss-flow state after the addition of the anti-loss-flow branch 5.

[0133] Substitute the known values ​​T2 = 95, Ts = 100, and TDC = 1.4664 into formula 1.

[0134]

[0135] Right now

[0136] The secondary hot water inlet temperature T1 = 92.67℃. At this time, the heat exchange power is:

[0137] Q=2.8×4.19×(95-92.67)=27.43KW

[0138] Load factor: 27.3 / 293.3 × 100% = 9.3%.

[0139] In other words, by adding the auxiliary drainage device to the anti-flow-loss branch 5, the flow-loss load rate can be reduced from 47.2% before the modification to 9.3%. Generally speaking, 30% is considered to be the lower limit of heating load demand. Therefore, this method reduces the acceptable load rate to 9.3%, which can prevent flow-loss in the heat exchange system.

[0140] The latent heat of saturated steam at 100℃ is 2257.2 kJ / kg, and the steam flow rate is 27.3 × 3600 / 2257.2 = 43.5 kg / h.

[0141] (III) Selection of Steam Trap

[0142] The selection of steam traps should not be based on the nominal diameter. Instead, the appropriate type of steam trap should be selected first based on the application, and then the model and diameter of the steam trap should be determined based on the system pressure, pressure difference, and condensate volume.

[0143] The selection method for auxiliary steam trap 502 is the same as that for main steam trap. From a safety perspective, it is required to meet the drainage requirements under low pressure differential conditions as much as possible. It is recommended to select float-type steam trap.

[0144] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the structure, process, method, etc. of the present invention without departing from the principles of the present invention are within the protection scope of the present invention.

Claims

1. A method for preventing water accumulation due to flow loss in a steam-water heat exchanger, characterized by the following: (i) By calculating the load, configure the temperature control system to ensure the pressure difference before and after the main drain valve, so that the generated condensate can be discharged from the steam-water heat exchanger (1) in a timely manner. Calculation of loss-of-flow condition for steam-water heat exchanger (1): a. Determine the heat exchange area based on the heat source temperature, user-end heat load, inlet and outlet water temperatures, and the heat transfer coefficient of the heat exchanger sample; b. Based on the selected area of ​​the steam-water heat exchanger (1), calculate the design operating conditions of the steam temperature, pressure, and steam flow rate of the steam-water heat exchanger (1); c. Calculate the working pressure and temperature of the steam-water heat exchanger (1) when condensate accumulates in front of the main drain valve by the back pressure after the main drain valve, and then determine the loss-flow condition. d. Calculate the heat load rate of the steam-water heat exchanger (1) under the loss-of-flow condition; 1) Introduce the temperature design constant TDC to determine the operating temperature inside the steam-water heat exchanger (1) under any load when the secondary fluid flow rate remains constant: Formula 1 Where: TDC: temperature design constant, Ts: saturated steam temperature inside the steam-water heat exchanger (1), T1: secondary fluid inlet temperature, T2: secondary fluid outlet temperature; The inlet and outlet temperatures of the secondary fluid can be obtained from Formula 1; 2) Calculate the heat exchange power using Formula 2: Formula 2 Where: Q: heat exchange power, m: mass flow rate; Cp: specific heat at constant pressure; : temperature difference of inlet and outlet water of secondary side of steam-water heat exchanger (1) The heat exchange power of the steam-water heat exchanger (1) is obtained from Formula 2, and then the heat load rate is obtained; (ii) Lower the installation position of the main drain valve assembly, and lead out a branch line (5) to prevent flow loss at point C between the steam-water heat exchanger (1) and the main drain valve assembly. Install an auxiliary drain valve (502) in the branch line (5) to directly discharge to the wastewater pipeline; the height difference h1 between point C and the main drain valve is ≥300mm; the height difference between point C and the outlet of the steam-water heat exchanger (1) is ≤1m; (iii) Determine the model and diameter of the main steam trap and auxiliary steam trap (502) based on the system pressure, pressure difference and condensate volume.

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