Preparation of plate heat exchanger before cleaning 2.1 scaling analysis of plate heat exchanger

Plate heat exchanger can be divided into two ways: water water exchange and steam water exchange. The water water exchange mode is water, and the temperature difference between cold and hot water is not large, which is about 70-90 ℃, and the scaling on both sides is basically the same; The heat medium of steam water exchange mode is water steam, which is not easy to scale in general. The cold medium is water, and the temperature is about 90 ℃, and it is easy to scale. The scale samples can be divided into scale and dirt, especially scale. The scale is mainly composed of various salts dissolved in water, which are decomposed by heat and the solubility is reduced, and the crystallization is deposited on heat transfer plate, which is usually carbonate, phosphate, sulfate and silicate. The scale is compact and hard to remove; The dirt is generally composed of fine particles of mud sand, dust, insoluble salt mud, colloidal hydroxide, debris, corrosion products, oil pollution, especially the body of bacteria and algae and their viscous secretion. This scale is large in volume, loose and soft in texture, and easy to remove.

2.2 selection of cleaning method and cleaning process for plate heat exchanger

The scale sample of plate heat exchanger is mainly water scale, which is hard, and is firmly combined with heat transfer plate, so it is difficult to remove it by physical method. Therefore, acid cleaning method in chemical cleaning is selected to remove scale. According to the fouling, aging degree and user requirements, the chemical cleaning of plate heat exchanger can be divided into two methods: disassembly cleaning and non disassembly cleaning. The cleaning and scaling removal is complete and the effect is good, but the work quantity is large and the process is complex, and it is easy to cause the leakage of heat exchanger and damage of parts and accessories; The cleaning and scaling are not complete enough, but the work quantity is small, the process is simple, and it is not easy to cause the leakage of heat exchanger, damage of parts and other adverse effects.

When the fouling of plate heat exchanger is serious, the heat exchange efficiency is low, and even blocked, * * it is required to be disassembled and cleaned; When the plate heat exchanger has a light scale or serious aging, it can be cleaned without disassembly.

The cleaning process of the combination of cycle cleaning and immersion cleaning can be adopted in chemical cleaning. The circulation cleaning is to use the circulating pump, the cleaning tank, the plastic pipe and the cleaning object to form a closed circulation system, add appropriate amount of cleaning agent to the circulation system, and use the circulating pump to clean it; Immersion cleaning is to turn off the circulating pump to soak after the detergent reaches a certain concentration in the circulation system.

In order to ensure the concentration of cleaning agent, the concentration of cleaning agent in the cleaning tank shall be detected every 1H during the cycle, so that the concentration of cleaning agent is kept in the effective range of 0.10-0.15mol/l * *, and the detergent shall be added if necessary. In case of noon or evening, it can be soaked and cleaned with detergent.

2.3 selection of cleaning agent

The heat transfer plate materials of plate heat exchanger are generally austenitic stainless steel, and the models are AISI304, 304L, AISI316, 316L and 316Ti. The stainless steel materials need to be cleaned with nitric acid based cleaning agent. The gasket materials are NBR 130-140, rb140 and EPDM 150. These materials can resist the corrosion of acid, alkali, ketone, alcohol and other solutions. Based on this, we adopt the special cleaning agent for stainless steel products developed by the Energy Research Institute of Henan Academy of Sciences (the cleaner has passed the technical appraisal organized by Henan Provincial Department of science and Technology), mainly composed of nitric acid, hydroxyacetic acid, corrosion inhibitor, penetrant, defoaming agent and other chemical agents. The cleaning agent has the characteristics of high scale removal rate, small corrosion rate and fast descaling speed, **The cleaning concentration is within 0.10-0.15mol/l. The performance indexes of the cleaning agent are in accordance with hg/t2387-2007 chemical cleaning quality standard for industrial equipment.