Plate heat exchanger

　　1. Introduction to Plate Heat Exchanger This complete set of equipment consists of a plate heat exchanger, balance tank, centrifugal sanitary pump, hot water device (including steam piping, hot water injector), support frame, and instrument box, etc. It is used for sterilizing and cooling milk or other heat-sensitive liquids. The material to be processed first enters the balance tank, is pumped into the heat exchanger by the centrifugal sanitary pump, and goes through preheating, sterilization, insulation, and cooling stages. Any material that does not reach the sterilization temperature is controlled by the instrument to redirect through a pneumatic return valve back to the balance tank for reprocessing. The sterilization temperature of the material is automatically controlled and continuously recorded by the instrument control box to monitor and check the sterilization process. This equipment is suitable for pre-sterilization and pasteurization of milk. The types of plate heat exchangers mainly include frame type (removable type) and brazed type, with the plate forms mainly being herringbone corrugated plates, horizontal flat corrugated plates, and bulged plates.

 

　　1.1 Basic Structure of Plate Heat Exchanger The plate heat exchanger mainly consists of two parts: the frame and the plates. The plates are thin sheets made from various materials, shaped into different forms of corrugation using various molds, and have corner holes for the flow channels of the medium. The edges of the plates and the corner holes are sealed with rubber gaskets. The frame consists of fixed pressing plates, movable pressing plates, upper and lower guide rods, and clamping bolts. The plate heat exchanger is assembled by stacking the plates between the fixed and movable pressing plates, which are then tightened with clamping bolts.

 

　　1.2 Characteristics of Plate Heat Exchanger (Comparison between Plate Heat Exchanger and Shell-and-Tube Heat Exchanger) a. High heat transfer coefficient Due to the interleaving of different corrugated plates, complex flow paths are formed, causing the fluid to flow in a rotating three-dimensional manner within the channels between the corrugated plates, which can generate turbulence at lower Reynolds numbers (generally Re=50~200), resulting in a high heat transfer coefficient, generally considered to be 3 to 5 times that of shell-and-tube exchangers. b. Large logarithmic mean temperature difference, small end temperature difference In shell-and-tube heat exchangers, two fluids flow separately in the tube and shell sides, generally in a counterflow manner. The correction factor for the logarithmic mean temperature difference is small, while plate heat exchangers mostly operate in parallel or counterflow, with a correction factor usually around 0.95. Additionally, the cold and hot fluids flow parallel to the heat exchange surface in plate heat exchangers, with no bypass flow. This results in a small end temperature difference for plate heat exchangers, with water heat exchange being less than 1°C, while shell-and-tube heat exchangers generally have a difference of 5°C. c. Small footprint The plate heat exchanger has a compact structure, with the heat exchange area per unit volume being 2 to 5 times that of shell-and-tube exchangers. It does not require space for withdrawing tube bundles for maintenance, thus achieving the same heat exchange capacity with a footprint of about 1/5 to 1/8 that of shell-and-tube heat exchangers. d. Easy to change heat exchange area or flow configuration By simply adding or removing a few plates, the heat exchange area can be increased or decreased; changing the arrangement of plates or replacing a few plates can achieve the desired flow configuration to adapt to new heat exchange conditions, while it is nearly impossible to increase the heat transfer area of shell-and-tube heat exchangers. e. Lightweight The thickness of the plates in plate heat exchangers is only 0.4 to 0.8 mm, while the thickness of the heat transfer tubes in shell-and-tube heat exchangers is 2.0 to 2.5 mm. The shell of the shell-and-tube heat exchanger is much heavier than the frame of the plate heat exchanger, which generally weighs about 1/5 that of the shell-and-tube type. f. Low cost Using the same materials and the same heat exchange area, the price of plate heat exchangers is about 40% to 60% lower than that of shell-and-tube exchangers. g. Easy to manufacture The heat transfer plates of plate heat exchangers are produced through stamping, with a high degree of standardization and can be mass-produced, while shell-and-tube heat exchangers are generally handmade. h. Easy to clean For frame-type plate heat exchangers, simply loosening the clamping bolts allows the plate bundle to be released, and the plates can be removed for mechanical cleaning, which is very convenient for heat exchange processes that require frequent cleaning. i. Low heat loss The only part of the plate heat exchanger exposed to the atmosphere is the outer shell of the heat transfer plates, so heat loss can be negligible, and insulation measures are not required. In contrast, shell-and-tube heat exchangers have significant heat loss and require insulation layers. j. Smaller capacity It is 10% to 20% of that of shell-and-tube heat exchangers. k. Higher pressure loss per unit length Due to the small gap between the heat transfer surfaces and the presence of protrusions, the pressure loss is greater than that of traditional smooth tubes.

　　1. Not easy to scale: Due to sufficient turbulence inside, scaling is not easy, with a scaling coefficient only 1/3 to 1/10 of that of shell-and-tube heat exchangers. 2. Working pressure should not be too high, and the medium temperature should not be too high to avoid possible leakage. Plate heat exchangers use sealing gaskets, and the working pressure generally should not exceed 2.5 MPa, with the medium temperature below 250°C; otherwise, leakage may occur. 3. Prone to clogging: The channels between the plates are very narrow, generally only 2 to 5 mm, making them prone to clogging when the heat exchange medium contains larger particles or fibrous materials. 1.3 Applications of plate heat exchangers: a. Refrigeration: Used as condensers and evaporators. b. HVAC: Intermediate heat exchangers used with boilers, intermediate heat exchangers in high-rise buildings, etc. c. Chemical industry: Soda ash industry, ammonia synthesis, alcohol fermentation, resin synthesis cooling, etc. d. Metallurgical industry: Heating or cooling of aluminum salt mother liquor, cooling in steelmaking processes, etc. e. Mechanical industry: Cooling of various quenching liquids, cooling of lubricating oil for reducers, etc. f. Power industry: Cooling of high-voltage transformer oil, cooling of generator bearing oil, etc. g. Pulp and paper industry: Heat recovery in bleaching processes, heating of washing pulp, etc. h. Textile industry: Cooling of viscose fiber caustic soda solution, cooling of boiling nitrated fibers, etc. i. Food industry: Cooling of juice sterilization, heating and cooling of animal and vegetable oils, etc. j. Grease processes: Soap base atmospheric drying, heating or cooling of various process liquids. k. Central heating: Heating of waste heat areas in thermal power plants, heating of water for bathing. l. Others: Petroleum, pharmaceuticals, shipping, seawater desalination, geothermal utilization. 1.4 Issues to pay attention to when selecting plate heat exchangers: 1.4.1 Plate type selection: The type of plate or corrugated style should be determined based on the actual needs of the heat exchange situation. For cases with large flow and allowed small pressure drop, a plate type with low resistance should be selected, and vice versa. Depending on the fluid pressure and temperature, determine whether to choose a removable or brazed type. When determining the plate type, avoid selecting plates with too small a single plate area to prevent excessive plate numbers, low flow rates between plates, and low heat transfer coefficients, especially for larger heat exchangers. 1.4.2 Flow and channel selection: The flow refers to a set of parallel channels in the plate heat exchanger where one medium flows in the same direction, while the channel refers to the fluid flow passage formed by two adjacent plates in the plate heat exchanger. Generally, several channels are connected in parallel or series to form different combinations of cold and hot medium passages. The flow combination form should be determined based on heat exchange and fluid resistance calculations, ensuring that the process conditions are met. Try to make the convective heat transfer coefficients in the cold and hot water channels equal or close to achieve the best heat transfer effect. When the convective heat transfer coefficients on both sides of the heat transfer surface are equal or close, the heat transfer coefficient reaches a larger value. Although the flow rates between the plates of the plate heat exchanger are not equal, the calculations for heat exchange and fluid resistance are still based on the average flow rate. Since the inlet and outlet pipes of the U-shaped single flow are fixed on the pressing plate, disassembly is convenient. 1.4.3 Pressure drop verification: In the design and selection of plate heat exchangers, there are generally certain requirements for pressure drop, so it should be verified. If the verified pressure drop exceeds the allowable pressure drop, redesign and selection calculations must be performed until the process requirements are met. Plate heat exchangers have high heat exchange efficiency, low material flow resistance loss, compact structure, sensitive temperature control, large operational flexibility, easy assembly and disassembly, and long service life. They can handle a wide range of materials, from ordinary industrial water to high-viscosity liquids, from food liquids and pharmaceutical materials with high sanitary requirements to corrosive acidic and alkaline liquids, and from liquid materials containing particulate powders to suspensions with a small amount of fibers. They can be used for heating, cooling, evaporation, condensation, sterilization, and heat recovery. For example, cooling generator sets and internal circulation of rectifiers; used in lubrication oil for metallurgy and mining machinery; sterilization of hydraulic stations, egg liquid, and edible oils; sterilization treatment of beer and wine; heat recovery in light textile and paper industries; collecting condensate, centralized heating; converting steam to water heating; intermediate heat exchange in boiler deoxygenation systems, etc. They are now widely used in metallurgy, mining, petroleum, chemical, power, pharmaceuticals, food, chemical fiber, light textile, paper, shipping, and centralized heating industries. Structural principle: The removable plate heat exchanger consists of many stamped corrugated thin plates arranged at certain intervals, sealed around by gaskets, and pressed tightly with a frame and pressing screws. The four corner holes of the plates and gaskets form the distribution and collection pipes for the fluid, while reasonably separating the hot and cold fluids, allowing them to flow in the channels on either side of each plate for heat exchange. Design features of plate heat exchangers: 1. High efficiency and energy saving: Its heat transfer coefficient is 3000 to 4500 kcal/m2•°C•h, which is 3 to 5 times higher than that of shell-and-tube heat exchangers. 2. Compact structure: The plates of the plate heat exchanger are closely arranged, occupying less floor space compared to other types of heat exchangers. A plate heat exchanger with the same heat transfer area is only 1/5 of that of a shell-and-tube heat exchanger. 3. Easy to clean and convenient to disassemble: The plate heat exchanger is clamped tightly by clamping bolts, making it easy to disassemble and clean at any time. Additionally, due to the smooth plate surface and high turbulence, scaling is not easy. 4. Long service life: The plate heat exchanger uses stainless steel or titanium alloy plates, which can withstand various corrosive media. The gaskets can be easily replaced, and maintenance is convenient. 5. Strong adaptability: The plates of the plate heat exchanger are independent components, allowing for flexible addition or reduction of flow paths, with various forms; suitable for various different process requirements. 6. No cross-contamination: The plate heat exchanger has a leakage channel set in the sealing groove, preventing different media from mixing. Even in the event of leakage, the medium is always discharged outward. Application range of plate heat exchangers: Plate heat exchangers have been widely used in metallurgy, mining, petroleum, chemical, power, pharmaceuticals, food, chemical fiber, paper, light textile, shipping, and heating sectors, suitable for heating, cooling, evaporation, condensation, sterilization, and heat recovery in various situations. Chemical industry: Manufacturing titanium dioxide, alcohol fermentation, ammonia synthesis, resin synthesis, rubber manufacturing, cooling phosphoric acid, cooling formaldehyde water, caustic soda industry, and electrolytic soda production. Steel industry: Cooling quenching oil, cooling electroplating liquids, cooling lubricating oil for reducers, cooling rolling machines, and wire drawing machine cooling liquids. Metallurgical industry: Heating and cooling of aluminum salt mother liquor, cooling of sodium aluminate, cooling of lubricating oil for aluminum rolling mills. Machinery manufacturing: Cooling various quenching liquids, cooling lubricating oil for presses and industrial mother machines, heating engine oil. Food industry: Sterilization and cooling of salt, dairy products, soy sauce, vinegar, heating and cooling of animal and vegetable oils, heating and cooling of beer and malt juice in beer production, sugar manufacturing, gelatin concentration, sterilization, cooling, and sodium glutamate production. Textile industry: Heat recovery of various waste liquids, cooling of boiling phosphoric fibers, cooling of viscose liquids, cooling of acetic acid and acid anhydride, cooling of caustic soda solutions, heating and cooling of viscose fibers. Paper industry: Cooling black liquor, heating and cooling of bleaching salt and alkali solutions, heat recovery of waste liquids from glass paper, heating cooking acids, cooling sodium hydroxide solutions, recovering waste liquids from bleaching paper, and condensing exhaust. Central heating: Heating of waste heat areas in thermal power plants, heating of domestic water, heating of boiler areas. Grease industry: Heating and cooling of synthetic detergents, heating of whale oil, cooling of vegetable oils, cooling of sodium hydroxide, cooling of glycerin, and emulsified oils. Power industry: Cooling of generator shaft pumps, cooling of transformer oil. Shipping: Diesel engines, central coolers, unloading sleeve water coolers, piston coolers, lubricating oil coolers, preheaters, seawater desalination systems (including multi-stage and single-stage). Others: Pharmaceuticals, petroleum, building ceramics, glass, cement, geothermal utilization, etc. The BR series products are assembled with two structures: a conventional structure (for infrequent disassembly and cleaning) and a suspended structure (for more frequent disassembly and cleaning). The conventional structure consists of herringbone corrugated plates, sealing gaskets, pressing plates, upper and lower positioning bolts, and pressing bolts. The suspended structure consists of herringbone corrugated plates, sealing gaskets, fixed pressing plates, intermediate plates, movable pressing plates, brackets, upper and lower positioning beams, and pressing bolts. Common faults: Plate heat exchangers have high heat transfer coefficients, small pressure drops, compact structures, light weight, small occupied space, convenient area and flow combinations, strong part universality, a wide range of selectable materials, and easy scalability in production. They have been widely used in food, machinery, metallurgy, petrochemicals, and shipping, becoming the dominant heat exchange equipment in urban centralized heating projects. To ensure the normal operation of plate heat exchangers and extend the service life of key components (such as plates and gaskets), it is particularly important to understand the faults that occur in plate heat exchangers, their causes, and treatment methods. 2. Common faults of plate heat exchangers: 2.1 External leakage: Mainly manifested as seepage (small amount, non-continuous water drops) and leakage (larger amount, continuous water drops). The main areas of external leakage are the sealing points between plates, the leakage groove of the second seal, and the inner side of the end plate and pressing plate. 2.2 Liquid mixing: The main feature is that the medium on the higher pressure side mixes into the medium on the lower pressure side, causing abnormal pressure and temperature in the system. If the medium is corrosive, it may also lead to corrosion of other equipment in the pipeline. Liquid mixing usually occurs in the flow guiding area or the second sealing area. 2.3 Excessive pressure drop: The pressure drop at the inlet and outlet of the medium exceeds design requirements, even many times higher than the design value, severely affecting the system's flow and temperature requirements. In heating systems, if the pressure drop on the hot side is too large, the primary side flow will be severely insufficient, leading to inadequate heat sources and failing to meet the required secondary side outlet temperature. 2.4 Heating temperature cannot meet requirements: The main feature is that the outlet temperature is too low and does not meet design requirements. 3. Cause analysis and treatment methods: 3.1 External leakage: 3.1.1 Causes: ① Insufficient clamping dimensions, uneven dimensions (the deviation should not exceed 3 mm), or loose clamping bolts. ② Some sealing gaskets have come off the sealing groove, the main sealing surface of the gasket has dirt, the gasket is damaged, or the gasket has aged. ③ Plate deformation or misalignment during assembly causes gasket running. ④ There are cracks in the plate sealing groove or second sealing area. Example: Several thermal stations in Beijing, Qinghai, and Xinjiang use saturated steam as the primary heat source for heating. Due to the high temperature of the steam, in the early stages of equipment operation when the system is unstable, the rubber sealing gasket fails at high temperatures, causing steam leakage. 3.1.2 Treatment methods: ① In a no-pressure state, re-clamp the equipment according to the clamping dimensions provided by the manufacturer, ensuring uniform dimensions, with a deviation of clamping dimensions not exceeding ±0.2N (mm) (N is the total number of plates), and maintaining the parallelism between the two pressing plates within 2 mm. ② Mark the leakage area, then disassemble the heat exchanger to check and resolve issues one by one, reassemble or replace gaskets and plates. ③ Disassemble the heat exchanger to repair or replace deformed plates. If there are no spare plates, temporarily remove the deformed plates and reassemble for use. ④ When reassembling the disassembled plates, clean the plate surfaces to prevent dirt from adhering to the gasket sealing surfaces. 3.2 Liquid mixing: 3.2.1 Causes: ① Improper selection of plate materials leading to corrosion and cracks or perforations in the plates. ② Operating conditions do not meet design requirements. ③ Residual stress after cold stamping of plates and insufficient clamping dimensions during assembly cause stress corrosion. ④ Minor leakage at the plate leakage groove causes harmful substances (such as Cl) to concentrate and corrode the plates, leading to liquid mixing. Example: In a sulfuric acid system of an aluminum company, a plate heat exchanger made of 254 SMo material experienced corrosion leakage of carbon steel connecting pipes on the cooling water side after 5 months of operation, with acid leaking into the cooling water side. Inspection revealed severe corrosion and cracking at the acid inlet and flow guiding area of the plates. On-site analysis found that the operating temperature, flow, and concentration parameters exceeded design conditions, with the operating temperature far exceeding the material's applicable range. Using saturated steam as the primary heat source for the plate heat exchanger can easily lead to plate corrosion during operation, resulting in product mixing. This is due to the high temperature of the steam, which can easily cause the rubber sealing gasket to fail at high temperatures, leading to steam leakage and rapid condensation in the second sealing area. As leakage continues, the residual condensate accumulates, forming a localized area with a high Cl concentration, reaching conditions that destroy the passivation layer on the plate surface. Additionally, due to the high internal stress formed during the cold stamping of the plates in this area, stress corrosion occurs when the surface passivation layer is destroyed. 3.2.2 Treatment methods: ① Replace plates with cracks or perforations, using a light transmission method to find plate cracks on-site. ② Adjust operating parameters to meet design conditions. ③ During maintenance and assembly of the heat exchanger, the clamping dimensions should meet requirements, and smaller is not always better. ④ Reasonable matching of plate materials. 3.3 Excessive pressure drop: 3.3.1 Causes: ① The operating system pipeline has not been properly flushed, especially in newly installed systems where many contaminants (such as welding slag) enter the plate heat exchanger. Due to the narrow cross-sectional area of the flow channels in the plate heat exchanger, sediments and suspended solids accumulate at the corners and flow guiding areas, significantly reducing the flow area and causing major pressure losses in these areas. ② The initial selection of the plate heat exchanger was too small, causing excessive flow rates between plates and large pressure drops. ③ After a period of operation, scaling on the plate surfaces leads to excessive pressure drops. Example: In 2000, our factory provided a BR10 type plate heat exchanger for a centralized heating system for a user in Xinjiang, designed for a primary supply water temperature of 130°C. During the design selection of the heat exchanger, the heat transfer coefficient was set too high, close to 5500 W/(m•K), while it should have been around 3500 W/(m•K). At the same time, the design unit overestimated the flow margin when selecting the pump, causing the flow rate of the secondary medium between the plates of the heat exchanger to exceed 1 m/s, resulting in an actual operating pressure drop of 0.2 to 0.3 MPa, severely disrupting the hydraulic balance of the secondary network. 3.3.2 Treatment methods: ① Remove contaminants or scale from the flow channels of the heat exchanger, and for newly operating systems, clean weekly based on actual conditions. When cleaning the plate surfaces of scale (mainly CaCO3), use a solution containing 0.3% amino sulfonic acid or a solution containing 0.3% urotropine, 0.2% aniline, and 0.1% potassium thiocyanate in 0.8% nitric acid, with a cleaning temperature of 40 to 60°C. When performing chemical immersion cleaning without disassembly, open the inlet and outlet of the cold medium in the heat exchanger, or install a DN25 cleaning port on the inlet and outlet connecting pipes during installation, inject the prepared cleaning solution into the equipment, soak, and then rinse with clean water to remove residual acid, ensuring pH ≥ 7. When disassembling for cleaning, soak the plates in the cleaning solution for 30 minutes, then gently scrub the scale with a soft brush, and finally rinse with clean water. During the cleaning process, avoid damaging the plates and rubber gaskets. If using a non-disassembly mechanical backwashing method, first connect a pipe to the inlet and outlet pipelines, connect the equipment to the mechanical cleaning vehicle, and inject the cleaning solution in the reverse direction of the medium flow, with a circulation cleaning time of 10 to 15 minutes, controlling the medium flow rate at 0.05 to 0.15 m/s. Finally, rinse several times with clean water, ensuring that the Cl concentration in the clean water is controlled below 25 mg/I. ② The secondary circulating water should preferably be softened, generally requiring that the concentration of suspended solids does not exceed 5 mg/L, with impurities not larger than 3 mm in diameter, and pH ≥ 7. When the water temperature does not exceed 95°C, the concentrations of Ca and Mg should not exceed 2 mmol/L; when the water temperature exceeds 95°C, the concentrations of Ca and Mg should not exceed 0.3 mmol/L, and the dissolved oxygen concentration should not exceed 0.1 mg/L. ③ For centralized heating systems, a method of one-time replenishment to the secondary side can be used. 3.4 Heating temperature cannot meet requirements: 3.4.1 Causes: ① Insufficient flow of the primary medium leads to a large temperature difference on the hot side and a small pressure drop. ② Low temperature on the cold side, with both cold and hot end temperatures being low. ③ Uneven flow distribution among multiple parallel plate heat exchangers. ④ Severe scaling inside the heat exchanger. 3.4.2 Treatment methods: ① Increase the flow of the heat source or enlarge the diameter of the heat source medium pipeline. ② Balance the flow of multiple parallel plate heat exchangers. ③ Disassemble the plate heat exchanger to clean the scale on the plate surfaces. 1. Main control parameters: The main control parameters of the plate water heater include the single plate heat exchange area, total heat exchange area, hot water output, heat transfer amount, heat transfer coefficient K, design pressure, working pressure, and thermal medium parameters. 2. Performance characteristics: (1) High heat transfer amount, with the heat transfer coefficient K ranging from 3000 to 8000 W/(m2•K), higher than other types of heat exchangers. (2) The high heat transfer coefficient of plate heat exchangers determines their compact structure and small volume, allowing for 250 square meters of heat transfer area to be arranged within one cubic meter of volume, greatly surpassing other types of heat exchangers. (3) Plate heat exchangers also feature flexible assembly and easy disassembly for cleaning, allowing for changes in heat exchange area by increasing or decreasing the number of plates to adapt to changes in thermal load. For relatively pure fluids, the number of flow paths can also be increased to improve flow rates between plates to achieve a high heat transfer coefficient. (4) Due to the use of two seals between the cold and hot media in plate heat exchangers, and the openings communicating with the atmosphere between the two seals, it effectively prevents the mixing of the two media. 3. Classification: Plate water heaters are mainly divided into corrugated plate plate water heaters, spiral plate plate water heaters, etc., based on different plate types. 4. Under the same heat consumption, the calculation formula for the water consumption corresponding to different temperatures of hot water: qr—hot water consumption (L/person•d); tr—hot water temperature; tL—hot water temperature. 5. Key points for product selection: 1. The control parameters for selecting plate heat exchangers include the material of the heat exchanger, working pressure, design temperature, etc. 2. When selecting heat exchangers, try to ensure that the side with a lower heat transfer coefficient has a higher flow rate, and try to make the heat transfer coefficients on both sides of the heat exchange surfaces of the two fluids equal or close to improve the heat transfer coefficient. The temperature of the fluid heated by the heat exchanger should be 10°C lower than the saturation temperature at the outlet pressure of the heat exchanger and should be lower than the working temperature of the pump used for secondary water. 3. Fluids containing sand and dirt should be filtered before entering the heat exchanger. 4. When selecting plate heat exchangers, the flow rate at the interface of the fluid on the side with a smaller temperature difference should not be too high, and it should meet the pressure drop requirements. 5. For cases with large flow and allowed small pressure drops, a plate type with low resistance should be selected; conversely, a plate type with high resistance should be selected. 6. Choose removable or welded types based on fluid pressure and temperature conditions. 7. Avoid selecting plates with too small a single plate area to prevent excessive plate numbers, low flow rates between plates, and reduced heat transfer coefficients. 8. The heat exchange medium of plate heat exchangers should not be steam. 6. Construction and installation key points: 1. The heat exchanger should not be deformed, and fasteners should not be loose or have other mechanical damage. 2. During equipment hoisting, the lifting rope should not be hung on the connecting pipes, positioning beams, or plates. 3. Leave enough space around the heat exchanger for maintenance. 4. The inlet and outlet connecting pipes for cold and hot media should be connected according to the direction specified on the factory nameplate. 5. The pipelines connecting to the heat exchanger should be cleaned to prevent sand, welding slag, and other debris from entering the heat exchanger and causing blockages. 6. The heat exchanger should undergo a water pressure test at 1.5 times the maximum working pressure, and the steam part should not be lower than the steam supply pressure plus 0.3 MPa, while the hot water part should not be lower than 0.4 MPa. 7. Standards: Product standard GB16409-1996 "Plate Heat Exchanger" Engineering standard GB50242-2002 "Construction Quality Acceptance Specification for Building Water Supply and Drainage and Heating Engineering" CJJ28-2004 "Construction and Acceptance Specification for Urban Heating Pipeline Engineering" 8. Related standard atlas 05R103 "Heat Exchange Station Engineering Design Construction Atlas"