Device control center in the region, winter heating heat exchanger in the laboratory building, transformation and distribution floor and part of the pumping station and dosing room station had been using a shell and tube heat exchanger. The heat carrier is 1.1MPa, 230 ° C steam; heat carrier is hot water, the water temperature was 92 ° C, return water temperature is 70 ° C, the water supply pressure is 0.5MPa, the backwater pressure is 0.14MPa. The original shell and tube heat exchanger equipment is obsolete, the amount of maintenance, and steam consumption have increased year after year. So during the overhaul in 2006, the original shell and tube heat exchanger transformed into a plate heat exchanger.
A plate heat exchanger
The plate heat exchanger (plateheatexchangers, or PHE) is a new high efficiency heat exchanger. His invention began in 187 years, primarily for the food industry, and later gradually extended to other industrial areas of the paper, pharmaceutical, metallurgy, mining, machinery manufacturing, electric power, shipbuilding, heating and petroleum chemical. Currently the world's better-known manufacturers of plate heat exchanger Sweden's Alfa-laval (Alfa Laval), SWEP (SWEP), Germany GEA Company, British APV, Japan's Hisaka (Japanese version). Plate heat exchanger consists of a series with some corrugated shape sheet metal is piled up due to its special structure, making the plate heat exchanger has the following advantages .
1.1 The overall heat transfer coefficient, small footprint devices
The plate heat exchanger plates are generally made of slotted corrugated medium flow was a complex three-dimensional flow structure within the flow channel, the flow direction and flow rate are constantly changing, causing great disturbances in the low Reynolds number (General Re = 50 ~ 200) can be induced turbulence (and tube heat exchanger is required Reynolds number reached 20 or more). Thinning of the liquid film thickness of large disturbances, prevent the adhesion of the impurities in the deposition of heat transfer surface, thereby reducing the fouling resistance, combined with the thickness of the plate 0.6 ~ 0.8mm, the thermal resistance smaller, the other in the plate for heat, cold and hot fluid from both sides of the plate by the fluid flow channel is smaller, does not appear that the bypass flow of the image tube shell heat exchanger, so the higher the overall heat transfer coefficient. If the water / water heat transfer medium, the overall heat transfer coefficient of the plate heat exchanger up to 8360 ~ 25080kJ/m2 · h · ℃ for 3 to 5 times of the shell and tube heat exchanger heat transfer coefficient, but the size of the equipment only tube for about 30% of the shell heat exchanger.
1.2 The heat transfer efficiency
The plate heat exchanger of the heat transfer efficiency is very high, there are many international companies to provide logarithmic mean temperature difference △ Tm = 1 ° C, the plate heat exchanger products. Minimum hot and cold logistics logarithmic mean temperature difference between a teenager led to the heat exchanger heat transfer area, from the engineering point of view, is not economic.
1.3 logarithmic mean temperature difference
Improve the logarithmic mean temperature difference of heat transfer is an important means of heat transfer enhancement effect. The fluid flow direction and the way will affect the logarithmic mean temperature difference. And flow or countercurrent fluid flow in general was a plate heat exchanger, the heat transfer to the mean temperature difference correction factor is usually about 0.95. Two kinds of fluid flow within the shell and tube shell and tube heat exchanger, the overall flow pattern of the cross-flow, mixed flow in the shell for multi-strand flow in the tube side, so pass thermal mean temperature difference correction factor is generally small (about 0.8).
1.4 assembly is flexible, flexible operation, convenient use and maintenance of plate heat exchanger by a number of plates assembled by simply increasing the reduction of the number of plate can easily adjust the size of the heat transfer area, and therefore very flexible to use, the operating elastic, and not image tube shell-and-so, you need to set aside a lot of space to pull out the tube bundle maintenance. The plate heat exchanger only need to loosen the clamping screw can be in the original space within the 100% exposure to the inverted surface heat exchanger plate, easy maintenance.
The applicable conditions of plate heat exchanger and the implementation of the program for heat transfer station
Plate heat exchangers have advantages, but it does not completely replace the shell and tube heat exchanger. One reason is that the plate heat exchanger cleanliness of the media are higher, and it requires the impurities in the medium particle diameter less than 1.5 ~ 2mm; plate and frame heat exchanger because the early (commonly known as the detachable plate change heat) is only applicable to the working pressure less than 1.6MPa, working conditions in the temperature range between 120 ~ 165 ℃.
Due to the heat exchanger station heat source is 1.1MPa; superheated steam of 230 ° C by the temperature limit of the gasket (common EPDM gasket temperature of 150 ° C, high temperature EPDM gasket temperature of 180 ° C, high temperature PTFE gasket temperature of only 220 ° C, and expensive, about eight times as high temperature EPDM gasket), the detachable plate heat exchanger does not apply to the working condition requirements.
Such as the use of brazed plate heat exchanger or laser all-welded plate heat exchanger, equipment costs (about 3 to 5 times) of the detachable plate heat exchanger price, and not removable, for easy maintenance.
Therefore, the final addition and subtraction of the program of the temperature of the device before the detachable plate heat exchanger, heat transfer less efficient in this scenario, but a higher temperature rating of shell and tube heat exchanger as a steam desuperheater , part of the heating return water (about 10% of the total backwater flow) superheated steam down to 150 ~ 180 ℃, after entering the plate heat exchanger to the rest of the heating return water heating, this program charge The use of the advantages of the two heat exchangers were at the same time heating the water side of the parallel operation mode than in series more effectively reduce the pressure drop, more energy-efficient, as shown in Figure 1.
Three main operating parameters
The main operating parameters in Table 1.
4 Technical Analysis
4.1 covers an area of
The structure of the plate heat exchanger is extremely compact, and less temperature device smaller (φ300; L = 1500), arranged at the top of the plate heat exchanger, plate heat exchanger organic combined into one, which covers an area of ？？only tube shell-and-about 1/4 of the heat exchanger.
4.2 The maintenance workload
Transformation of the former, each run cycle, due to the shell and tube heat exchanger fouling, the effect of heat transfer significantly reduced need dismantling, cleaning shell and tube heat exchanger, and maintenance, demolition of the insulation, core pulling such as workload. Transformation run after two cycles after the demolition inspection and disassembly is very convenient, only need to loosen the clamping screw, exposing the plates can be cleaned.
4.3 pressure loss
In the case of an equality of heat carrier flow, significantly lower pressure drop through the heat exchanger, the water pressure from 1.4MPa to 1.6MPa.
4.4 The steam consumption
Steam consumption decreased from 1.11kg / s down to 0.97kg / s per hour, saving steam: (1.11-0.97) × 3600/1000 = 0.504t.
4.5 The effect of heat transfer
Steam consumption is reduced, the heat transfer is greatly improved, the water temperature from 92 ℃ to 95 ℃.
5.1 The maintenance costs
The dismantling of the original shell and tube heat exchangers, removable insulation, core pulling, cleaning, etc. Total cost: $ 5000 to overhaul the plate heat exchanger and the temperature reduction unit Total cost: 1000 yuan. Before the transformation, each run cycle maintenance, transformation after every two run cycle maintenance. Therefore, the transformation of each run cycle can save on maintenance costs :5000-1000/2 = 4500
5.2 The steam costs
Savings per hour of steam 0.504 t per run cycle five months, each run cycle can save steam: 0.504 × 24 × 30 × 5 = 1814.4t
Calculated by steam costs 120 yuan / t, each run cycle can save steam costs: 1814.4 × 120 = 217 728.
5.3 Total cost savings
Transformation before and after each operation cycle cost savings Total: 217 728 +4500 = 222,228 yuan
Prove after two cycles of the actual operation of addition and subtraction temperature device using a removable plate heat exchanger to replace the traditional shell and tube heat exchanger, reliable operation, the actual operating parameters meet the design requirements, as opposed to brazed plate heat exchanger or laser welded plate heat exchanger, greatly reduces the total investment, and compared with the traditional shell and tube heat exchanger, but also greatly reduces energy consumption and maintenance costs of the heat exchange station.