Almost every process facility requires steam. It is used for heating, drying, power, etc. Steam is an excellent way to convey energy from one process to another. The heat and energy of the steam needs to be measured and controlled into the next stage of the process.
Steam flow and pressure is controlled with an orifice. You can use a fixed orifice, a line sensed pressure regulator, or a full control valve. There is no adjustment with an orifice. A regulator is given a fixed output setpoint, but is not adjustable by the control system. A control valve can vary the orifice size according to the output of the control system which has measured the flow, pressure, and/or temperature from process instrumentation and sensors.
When controlling system, it is always done with an orifice which creates a pressure drop. The higher the flow rate and pressure drop, the noisier the valve will be. There are two problems with noise. First is the loud environment and potential damage to your hearing. The second is that noise is vibration and that vibration can damage the physical components of the valve. 85dB or lower is the ideal noise level. You can avoid high noise by taking the pressure down in small increments rather than one big drop. This can be accomplished within a control valve or through a fixed drop low decibel cassette inline with the control valve.
There is a way to make almost every steam control application low noise and highly reliable. You must select the proper method of controlling and regulating the steam with the proper number of pressure drops. For help with your next steam application, please contact us.
I have had several questions come up in the last couple of days about where to mount differential pressure transmitters in relation to the pipe mounted flow element. There are three different types of fluids that you will want to measure and they require different mounting methods.
First, is dry gases. The DP transmitter must be mounted vertically above the pipe taps so that all potential liquid or condensation in the line will drain back into the pipe.
Second is liquids. The DP will be mounted vertically below the pipe so that the line will always stay full with liquid.
The third is condensing liquids such as steam. These require that the DP transmitter is mounted below the pipe taps, but they must have a vertical water column that is always filled with the same amount of condensate so that the water pressure on the impulse lines remains consistent. The water column will block the high-temperature steam from cooking your transmitter. If you mount it above the pipe and there is no water present, the 300F+ heat will break your transmitter.
This was a very short and basic introduction to mounting and configuring your DP flow system. For more info and a thorough explanation, please contact me via this site.
Oh Crap! All hands on deck! You’re in another unplanned outage and you are working 16 hour days trying to get the plant up and running again. This time it was a broken agitator shaft, but you’ve dealt with other equipment failures and operator error in the past. Regardless of what caused the outage, you are stuck working to fix it and get back up. Outages are a pain and they are expensive. You have to pay your people overtime to get the problem fixed. You have to spend big dollars to replace/repair the broken equipment. You are also not making any product and therefore not making any money. It’s a trifecta of terrible. What if we could take steps to minimize unplanned downtime? Would you do these steps or at least some of them? I think it is worth it to find the time when things are running well to prevent things from going badly.
First, you must figure out the potential failure points in the plant. On a grand scale it could be three things. Operator error, loss of utilities, or equipment failure (there could be more, but for the sake of this article, let’s go with those three).
In regards to operator error, can you predict what an operator could do to damage or shut down the process? If you can, then implement control system or SOP fixes to prevent them from being able to that damaging activity. Noone wants to shut down a plant, but accidents can happen. Take steps in the software to prevent those accidents.
Regarding the loss of utilities, I don’t know that there is much you can do. You could keep a spare transformer or other large utility items as spares, but these events are relatively rare and it would be really hard to predict which component (yours or the utilities) would fail.
Lastly you have equipment failure. This is preventable or at least predictable. We all do preventative maintenance. Do you do predictive maintenance? Changing oil in gear boxes and replacing consumable parts on a regular basis prevents unplanned down time, but what if there is something that doesn’t get these PMs that fails? What if you could predict this failure? instrumentation has a lot of diagnostic information ready to be used already. You just have to look and have I/O capable to reading and logging that data. You could also use a smart cloud service (like Siemens) to analyze that data for you. There are also SIL (Safety Integrity Level) devices and equipment. These have proven and tested and predictable mean time to failures and can be used to ensure the safe and reliable function of your process. Keeping spare parts and complete assemblies for all your critical components is worth the inventory cost, espessially if you will lose enough paying idle people, not making product, and paying expedite fees to ship an emergency part in from somewhere else.
So, while you are stuck in this unplanned shutdown, use this as an opportunity to make some changes to your inventory, SOPs, and data analysis to prevent the next one. If I could do a little work and spend a little money now to prevent spending a lot of money and doing a lot of work later, I would.
If you like this article (or not) leave a comment and let me know what you think. I will try to cator future articles to the interest of my readers.
