When there are fibers and large particles in the heat exchanger, the effect of backwashing the device is quite obvious. Backwashing can be achieved in one of the following two ways:
(1) Flush the device with clear water in the opposite direction to normal operation.
(2) Arrange pipelines and set valves on the pipelines so as to operate in reverse mode at the product side within a fixed time. This special mode is especially suitable for heat exchangers whose products are steam.
(3) When the water flow contains a considerable amount of solid or fiber substances, it is recommended to install a mesh filter on the water supply line in front of the heat exchanger. This can reduce the number of backwashing.
The principle of on-site cleaning
(1) Never open the heat exchanger when it is still hot, under pressure, carrying liquid or in operation.
(2) Clean water must always be used for flushing operations. (The water should be free of salt, sulfur, chlorine or iron ions).
(3) If steam is used as sterilization medium, the steam temperature of NBR gasket shall not exceed 120℃ and that of EPDM gasket shall not exceed 140℃.
(4) If chlorine-containing solution is used as cleaning medium, the solution with the lowest concentration should be used at the lowest temperature as far as possible. The time for cleaning the plate with this solution should be minimized as far as possible. The concentration of chlorine in the solution cannot exceed 100×10-6, the temperature of the solution must be lower than 37℃, and the contact time between the plate and the solution cannot exceed 10min.
(5) Concentrated cleaning solution must be added before water circulates through the device. Never inject these solutions during water circulation.
(6) Centrifugal pumps must be used to keep the cleaning solution circulating.
(7) Do not use hydrochloric acid to clean the plate.
(8) After cleaning the plate with any type of chemical solution, the plate must be thoroughly washed with clear water.
Matters needing attention in plate cleaning
(1) Do not wash stainless steel plates with hydrochloric acid or water with chloride concentration exceeding 300×10-6.
(2) Do not use phosphoric acid or sulfuric acid to clean titanium plate.
(3) usually the concentration of cleaning solution should be below 4% (except for special cases), and the temperature of cleaning solution should not exceed 60℃.
