Sterilization

With the rising cost of all utilities, a facilities planner or purchaser of sterilization equipment must be cognizant of the operating costs, not just the purchase price.

With the rising cost of all utilities, a facilities planner or purchaser of sterilization equipment must be cognizant of the operating costs, not just the purchase price. Two of the principle culprits are the steam usage/generation and water usage. The water used to generate steam ends up down the drain. In addition, it must be cooled before it can enter your PVC drain. Think of the entire cycle: you pay for the water, you pay to heat it, then you pay to cool it, then you pay to get rid of it. Water is not cheap!

House Steam, Local Steam, or Both

Determining the steam source for your steam sterilizer is usually a foregone conclusion. “House steam” is the most economical choice, however if this source is unavailable, an electric generator is the answer. Have you considered both? The advantages, drawbacks, cautions, and options are discussed below.

House Steam Source

Assumption: Sufficient supply, proper pressure (usually 50-80 psig), and high quality.

High quality requires that the steam is clean and dry. If you have “wet” or “dirty”steam then you must provide a trap prior to it entering the sterilizer system. The trap will condense the moisture and it needs to be piped to drain. A trap with a filter is superior, as it will keep the particulates from entering the steam lines.

Why are these concerns so important? Facilities typically use iron pipe to transport steam from a central boiler to the points of use. If the steam is wet or dirty, rust will build up in the lines over time. If this fouling is not addressed, then the rust enters the piping, valves, and chamber of the sterilizer. Rust in the piping and valves will lead to buildup and cause inconsistent operation and/or failure of valves. The particulates will act as abrasives as they flow through the valves and wear the seat and packing causing premature failure. This same rust will enter the jacket and chamber resulting in contamination of the products being sterilized or experiment being run. Again, the solution is to add a trap and filter to the incoming steam line (these systems are readily available).

Local Electric Steam Source

If house steam is not available, or the cost to run new pipes is prohibitive, then a steam generator local to the sterilizer is the logical choice. It is usually mounted under the sterilizer to save space and minimize piping. The internal heaters are electrically powered with available (and prudent) voltage/current. You would not want to power a 39kW boiler with 117 VAC, as it would draw over 300 amperes.

An electric steam generator or boiler needs a water supply. Unless distilled water is required by the manufacturer, normal cold water is usually acceptable. The concern when using a boiler is the buildup of sediment and impurities within the boiler chamber due to water hardness. The solution is to “blow down” or empty the water out of the chamber weekly. This cleaning can be done manually or automatically. A good time to perform this function is when the system has been shut down at the end of the day. An advantage of the automatic shutdown is that it will occur without any human interaction thus insuring that it is done on a regular basis. It is very important that the steam be cooled prior to entering the drain. PVC is rated at 140°F and if the steam is going to a septic system, it needs to cool further.

In a manual operation “blow down,” a cold water line must be opened to mix with the outgoing steam. If the system has a steam cooling option, then the generator drain line is piped into the steam-cooling module. The generator drain line may need a reducing valve to insure the steam from a fully pressurized generator will not overwhelm the cooling system and prevent proper cooling.