Heating plate heat exchanger

Heating plate heat exchangers are commonly used in heating systems such as heat exchange stations and livestock waste heat recovery. For different types of heat sources, this plate heat exchanger can choose detachable heat exchangers or fully welded heat exchangers.

1、 Selection of Heating Plate Heat Exchanger
At present, the primary heat medium temperature used in urban centralized heating in China is generally 130 ℃/70 ℃, and the secondary heat medium temperature is 95 ℃/70 ℃ or 85 ℃/60 ℃. In this case, the flow rate in the primary heat medium channel of the plate is only about half of the flow rate in the secondary heat medium channel. For symmetrical flow channels, if the primary heat medium flow rate is about 50% of the secondary heat medium flow rate, the convective heat transfer coefficient between the fluid and the plate in the primary heat medium flow channel is about 70% of that in the secondary heat medium flow channel. Therefore, when the primary and secondary side medium flow rates are large, it is advisable to use non symmetrical plate heat equipment.

2、 Problems in the operation of plate heat exchangers for heating
1. Corrosion of heating plate heat exchanger:Although the plates of the plate heat exchanger are made of stainless steel and have strong corrosion resistance, high levels of chloride ions in water can cause corrosion; Water and oxygen are also necessary conditions for the corrosion of heat exchanger plates. If the corrosion occurs uniformly on the entire metal surface, the corrosion rate will not accelerate and the harm it brings will not be too great. However, if the corrosion is concentrated in certain parts of the metal surface, the corrosion rate will accelerate and rust through is prone to occur, which is very harmful. It will not only reduce the efficiency of equipment work, but also greatly shorten the service life of equipment and increase maintenance costs. In addition, due to the generation of corrosion, the metal materials of the heating system will be damaged, causing serious corrosion and leakage of pipelines and end equipment, and in severe cases, even leading to the premature scrapping of plate heat exchangers and boilers. So, the water quality indicators of circulating water are very important.

2. Scaling and blockage of heating plate heat exchanger
In the central heating system, the circulating water for the heating network is generally tap water and deep well water, which have high hardness. When the water reaches the boiling point, precipitation will occur in the pipe network. Due to the small flow surface of the plate exchange and the relatively low flow velocity between plates, the sediment is prone to form scale on the hot side or suspend in the circulating water, and then deposit on the surface of the heat exchanger, forming secondary scale, affecting water quality, and causing scaling and blockage of the heat exchanger. Due to the low thermal conductivity of the fouling layer, the heat transfer resistance is greatly increased, thereby reducing the heat transfer efficiency of the heat exchanger. When a fouling layer forms on the surface of a heating plate heat exchanger, it will reduce the flow area of the equipment, increase the resistance of fluid flow through the equipment, and consume more pump power, resulting in unnecessary cost waste.

3、 Solve the problems in the operation of heating plate heat exchangers
1. Corrosion prevention and cleaning
If the chloride ion content in the water exceeds 200ppm, ordinary stainless steel plates should not be used when selecting plate heat exchangers. A series of effective measures can be taken to reduce the chloride ion content in the primary and secondary network media, keeping it within a reliable concentration range. However, for the entire centralized heating system, this method is costly and difficult to manage. Generally speaking, for systems that use a lot of stainless steel materials, the chloride ion content should be controlled below 300mg/L, and strictly controlled below 50mg/L. Caustic soda can be evenly added during the operation of the heating system to increase the pH value of the circulating water and control it at a stable level. After this treatment, the effectiveness of scale and corrosion inhibitors will also be greatly improved. Correctly clean plate heat exchangers and determine the cleaning method. For stainless steel materials, strong acid is generally used as the cleaning agent, and hydrochloric acid cannot be used. During the cleaning process, try to reduce the cleaning time and soaking time as much as possible, which should be less than 2 hours. During the soaking period, the corrosion rate and scale inhibition rate of the cleaning mother solution should be tested in stages to avoid corrosion of the plate heat exchanger; No matter which cleaning solution is used, the heat exchanger should be completely rinsed with clean water after cleaning to remove residual cleaning solution and avoid secondary corrosion.

2. Prevent scale and solid impurities
If a sodium ion exchanger is used to treat the supplementary water, it is necessary to ensure that the hardness of the supplementary water meets the water quality standards, and strictly test the technical indicators such as hardness, suspended solids, and pH value of the circulating water in the heating system to effectively prevent the formation of calcium and magnesium scales. If tap water is used as the supplementary water, scale and corrosion inhibitors should be added to the water during the treatment process to ensure that the corrosion rate and scale inhibition rate of the inhibitors meet the requirements. In the actual production process, the amount of scale and corrosion inhibitors added should be regularly checked and tested to avoid scaling caused by insufficient addition or waste or corrosion caused by excessive addition.

The solid impurities in circulating water mainly include rust sludge, mud sand, residue, copper oxide, and biofouling. In order to eliminate or reduce the content of suspended solids and other impurities, the suspended solids content in the heating system should be controlled at 2-5mg/L. For well treated circulating water systems, the suspended solids content in the supplementary water should not exceed 0.5-1.0mg/L, while the suspended solids content in the circulating water of plate heat exchanger systems should be less than 10mg/L; Add filters to the return and makeup water pipelines to filter out some larger suspended impurities; Strengthen construction supervision and management. After the installation of each section of large-diameter pipelines, construction personnel should be organized in a timely manner to clean up welding slag and welding rods, and cleaning should also be carried out after the construction is completed; During daily operation, it is necessary to strengthen management and regularly discharge pollutants to reduce suspended impurities.