Steam sterilization is to place the product in the sterilization cabinet, and the heat released by the high temperature steam will lead to the coagulation and denaturation of the bacterial protein to achieve the purpose of sterilization. The characteristics of pure steam sterilization is strong penetration, protein, protoplasmic colloid in the humid and hot conditions for denaturation and coagulation, enzyme system is easy to destroy, steam into the cell condensation into water, can release potential heat to improve the temperature, but also enhance the sterilization force.
Air extraction equipment is used in the closed sterilization cabinet to extract air and other non-condensable gases. Because the existence of non-condensable gases such as air not only hinders the transfer of heat, but also hinders the penetration of steam to the product.
The steam sterilization temperature is the primary steam parameter controlled by the sterilizer. The thermal tolerance of various bacteria and microorganisms varies from species to species, so the required sterilization temperature and action time vary according to the degree of contamination of the sterilized item. The sterilization temperature of the product also depends on the heat resistance of the product itself and the damage effect of high temperature on some characteristics of the product.
Generally speaking, in order to ensure the heating efficiency and shorten the sterilization interval, the higher the sterilization temperature, the shorter the sterilization time. Steam temperature detection often has certain inhomogeneity, at the same time, the detection of the temperature deviation, has certain hysteresis and considering the saturated steam temperature and pressure of one-to-one relationships, relative steam pressure testing more even and rapid detection, and thus the sterilization steam pressure sterilization cabinet as control, and the sterilization temperature detection as a security guarantee.
In practice, the steam temperature and sterilization temperature may sometimes be different. On the one hand, when the steam contains more than 3% of the condensate water (97% dryness), although the temperature of the steam reaches the standard, the temperature of the steam will gradually decrease after passing through the condensate film due to the obstruction of heat transfer caused by the condensate water distributed on the surface of the product, so that the actual sterilization temperature of the product will be lower than the requirement of sterilization temperature. Especially boiler water, the water quality may contaminate sterilized products. So usually in the steam inlet using Watt DF200 high efficiency steam separator will be very effective.
On the other hand, the existence of air will have another impact on the sterilization temperature of steam. When the air in the chamber is not excluded or not completely excluded, the existence of air will form a cold point, making the products attached to the air can not reach the sterilization temperature. On the other hand, by controlling the steam pressure to control temperature control mode, the existence of air partly partial pressure, the pressure gauge shows that mixed gas pressure of total pressure.The actual steam pressure is lower than the required sterilized steam pressure.Therefore, the steam temperature can not meet the requirements of sterilization temperature, resulting in failure of sterilization.
Steam superheat is an important factor affecting steam sterilization, which is often ignored.EN285 requires that the superheat of sterilized steam should not exceed 5℃.The principle of saturated steam sterilization is that the steam condenses when the product is cold and releases a lot of latent heat energy, which makes the temperature of the product rise.While condensing, its volume shrinks sharply (1/1600), creating local negative pressure that allows subsequent vapor to penetrate the item.
Superheated steam, its nature is equivalent to dry air, its heat transfer efficiency is low;On the other hand, the superheated steam releases sensible heat and does not condense when the temperature drops to the saturation point, and the heat released at this time is very small, so that the heat transfer can not meet the requirements of sterilization.This phenomenon is obvious when the temperature is above 5℃. Steam overheating can also lead to rapid aging of items.
If the steam used is heat network steam for power generation, it is superheated steam itself.In many cases, even if the self-contained boiler produces saturated steam, the steam decompression in front of the sterilizer is an adiabatic expansion, making the original saturated steam into superheated steam.This effect is evident when the differential pressure exceeds 3bar.If the superheat exceeds 5℃, the watt water bath saturated steam device is preferred to eliminate the superheat in time.
The steam design of sterilization cabinet includes super steam filter, high efficiency soda separator, steam pressure regulating valve and water trap. Watt pilot steam pressure reducing valve can stabilize the steam pressure in a variety of conditions.The basic structure of the sterilization cabinet is generally the air inlet is on the top and the exhaust is on the bottom.Because the molar number of steam is smaller than that of air, the steam is fed into the sterilizer, and the cold air is gradually extruded from the upper to the lower vent and discharged.
The drain in the sterilization cabinet chamber must be timely and effective, and it can continuously exclude non-condensable gas when it is working. Watt thermostatic trap is preferred. If it is a jacketed sterilization pot, the jacketed steam drain must be timely and fast, and the watt inverted bucket trap is preferred.
Compared with other sterilization measures, steam sterilization is more efficient. In the production of traditional Chinese medicine, the pressure steam sterilization method can be used to sterilize heat-resistant rhizome Chinese herbal medicine pieces. The hard Chinese medicinal materials can be sterilized by ethanol pressure steam.