By Andrew Perks
I am sure there will be lots of stories in the days to come of these challenging times, but in the meantime, we need to look at how we can protect our equipment and maintain the cold chain.
Well, I have just had a month of it what with power-shedding and my computer crashing. Last year it was water availability in the Cape, now it’s power — our poor refrigeration plants really don’t know what’s going on. I feel really sorry for those owners with plants that don’t have a standby generator. The big issue is, where is the ‘light at the end of the tunnel’? The sad truth is, without power, there isn’t one …
It’s very important that we look at protecting our refrigeration equipment and maintaining the cold chain. As we all know, the process of refrigeration is the removal of heat from an object. To do this, we need to introduce a medium into the cooling space that is colder than the product being cooled. To get the right temperature of the refrigerant, we need to get it to the right pressure, and to do this we need to run compressors — a bit difficult if we have no electricity.
Then of course once we have removed the heat from the object, we need to reject it out of the system. With the larger ammonia systems, we need water to remove the rejected heat and condense the refrigerant to a liquid. Also complicated if we have no water or electricity.
When, and some say if, the electricity supply returns, we need to be extremely careful on restarting the system. It has to be sequential or the entire site’s electrical circuit will come under extreme pressure, resulting in overloads and circuit breakers tripping. These power surges are also affecting sensitive instrumentation. This requires the individual contractor to produce standard start-up operating procedures for the particular plant. This procedure is not simply switch on and go. We would not recommend that non-skilled or non-certified South African Qualification and Certification Committee for Gas (SAQCC Gas) technicians perform this action. Starting up a plant with a heavy system load requires competence and knowledge — there are so many intangibles that come into play.
This brings us back to the current situation of skills shortages in South Africa. There are just not enough contractors to go around, so clients need to invest in training their own staff. The solution could be pre-set and programmed start up sequences that rigidly conform to set parameters whilst monitoring plant operating conditions. No matter what, we can expect peak cooling loads as soon as the plant is restarted.
Peak power usage is associated with high ambient temperature and humidity conditions. It may be necessary to restrict cooling availability until the ambient temperatures start to drop in the evening, allowing your plant to go fully online when it starts to find a balance between capacity and ambient conditions. But who makes that call? Best to have a sequential balanced capacity control system in place. There are people and control systems out there that can assist users with these issues. But as usual, there are costs involved that could prove prohibitive.
So, how do we cope? I have been to some farms that are in the process of massive solar panel installations; others that are installing very large generating capacity on site. Now as you know, this is very expensive and somewhere in the selling price of the product, this has to be recouped. Nett result: up goes the cost to us, the customers.
One cannot help but ask how we ever got into this mess. With a growing nation and diminishing service availability, it’s a recipe for disaster.
Hopefully next month the message will carry a bit more encouragement …
