Steam Quality Requirements for In-house Steam Systems
PRIMUS often encounters steam sterilizer installations where inadequate steam quality being provided by in-house boilers causes unnecessary issues such as wet packs.
Steam should be presented to the steam sterilizer with the following characteristics:
- In the correct quantity
- Within the required temperature and pressure range
- Free from air and non-condensable gases
- Clean
- Dry
Correct Quantity of Steam
The correct quantity of steam must be made available for any heating process to ensure that a sufficient heat flow is provided for heat transfer.
Steam loads must be properly calculated and pipes must be correctly sized to achieve the flow rates required.
Correct Pressure and Temperature of Steam
Steam should reach the steam sterilizer at the required pressure and temperature. The correct sizing of pipework and pipeline ancillaries will ensure this is achieved.
Air and Other Non-condensable Gases
Air is present within the steam supply pipes and equipment at start-up. Even if the system were filled with pure steam the last time it was used, the steam would condense at shutdown, and air would be drawn in by the resultant vacuum.
When steam enters the system, it will force the air towards either the drain point, or to the point furthest from the steam inlet, known as the remote point. Therefore, steam traps with sufficient air venting capacities should be fitted to these drain points, and automatic air vents should be fitted to all remote points.
Cleanliness of Steam
Layers of scale found on pipe walls may be either due to the formation of rust in older steam systems, or to a carbonate deposit in hard water areas. Other types of dirt which may be found in a steam supply line include welding slag and badly applied or excess jointing material, which may have been left in the system when the pipework was initially installed. These fragments will have the effect of increasing the rate of erosion in pipe bends and the small orifices of steam traps and valves.
For this reason it is good engineering practice to fit a pipeline strainer (as shown below). This should be installed upstream of every steam trap, flowmeter, pressure reducing valve and control valve.
ADD PHOTOS
Steam flows from inlet A through the perforated screen B to the outlet C. While steam and water will pass readily through the screen, dirt will be arrested. The cap D can be removed, allowing the screen to be withdrawn and cleaned at regular intervals.
When strainers are fitted in steam lines, they should be installed on their sides so that the accumulation of condensate and the problem of waterhammer can be avoided. This orientation will also expose the maximum strainer screen area to the flow.
Dryness of Steam
Incorrect chemical feedwater treatment and periods of peak load can cause priming and carryover of boiler feedwater into the steam mains, leading to chemical and other materials being deposited onto piping and valve seats. These deposits will accumulate over time, gradually reducing the efficiency of the plant and causing significant problems with sterilizer performance.
In addition to this, as the steam leaves the boiler, some of it must condense due to heat loss through the pipe walls. Although these pipes may be well insulated, this process cannot be completely eliminated.
The overall result is that steam arriving at the sterilizer is relatively wet, and the droplets of moisture carried along with the steam can erode pipes, fittings, and valves.
A steam separator in the steam line before entering the sterilizer will greatly help remove moisture droplets entrained in the steam flow, and also any condensate that has gravitated to the bottom of the pipe.
In the separator shown below, the steam is forced to change direction several times as it flows through the body. The baffles create an obstacle for the heavier water droplets, while the lighter dry steam is allowed to flow freely through the separator.
A Steam Separator
Please see attached drawing for recommended installation of a separator and bucket trap for all steam sterilizers using in-house steam.
Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at dschall@spire-is.com.
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