The Cost of a Continuous Waste Stream in Process Automation

The following tip is from the ISA book by Greg McMillan and Hunter Vegas titled 101 Tips for a Successful Automation Career, inspired by the ISA Mentor Program. This is  Tip #43.

101 Tips for a Successful Automation CareerWhen an engineer starts his or her first job, he is often looking to make a name for himself in the plant. Saving the company big money and getting an award and/or recognition is a pretty good place to start. Amazingly, unnoticed money saving opportunities are often staring everyone in the face.

Concept: For example: a small 0.5 GPM purge can flow nearly 263,000 gallons in a year. Small air leaks and leaking steam traps can waste thousands of dollars a year and create an undue burden on utility systems. Fixing these mundane problems can be a cheap and easy source of significant savings.

Details: Plants inevitably deteriorate as they age. Because problems develop slowly and soon become familiar, plant personnel often fail to notice slowly developing air line leaks, sticking steam traps, and minor valve leaks throughout the facility. However, these problems can needlessly waste tens of thousands of dollars a year. Consider a steam trap that continuously leaks a tiny flow of 20 #/hr of 600 psi steam. This trap will leak 20 #/hr × 24 hr/day × 365 day/yr = 175,000 pounds of 600 psi steam a year! Figure the cost of that steam plus the cost of throwing away 175,000 pounds of hot, chemically treated boiler feed water and that single, very small steam leak will waste about $2200.00 a year.

Any continuous waste stream can cost a company a huge amount of money and be a source of potential savings. Look for such things as continuous water purges to pump seals that do not have to run all the time, especially if those seal flows contribute to the overall waste stream of the plant. If the plant is considering an air compressor size increase, it may be possible to avoid having to replace the existing unit by simply working through the plant and eliminating air leaks. Any steam leak is an excellent source of savings because the leak is not only a waste of steam but also a waste of condensate along with the heat energy in that condensate. Ultrasonic leak sensors can quickly locate many steam and air leaks even at a distance.

Watch-Outs: Plant personnel will occasionally make an equipment change to address a problem in the middle of the night with no thought to the long term impact of the modification. Here are some “late night” impromptu fixes that seem great in the short term but can have long term implications for unnecessary waste if left in place:

• A condensate pump fails in the middle of the night so Operations just opens a valve and lets the condensate drain out of a reboiler to the deck in order to keep the exchanger in service.

• A pump bearing is overheating so the operator throws a water hose on the pump to keep the bearing cool.

• Heat trace fails on a line so Maintenance winds some steam tubing around the line and crimps the end to let it blow and keep hot.

Any of these changes solves the problem at hand but if left in place they may ultimately waste thousands of dollars. If “temporary” fixes are implemented by Maintenance and/or Production that involve such things as continuous purges, be sure to follow up and make certain they ARE temporary.

Exceptions: Do not immediately assume that every purge or continuous flow can be eliminated. There may be a very good reason for that flow and removing it could have detrimental consequences to the process. Always ask the operators and/or production supervision about the flow to find out why it exists.

Insight: Many steam trap vendors will offer to do a free or very low cost “steam trap survey” to locate leaking steam traps in your facility. Obviously they are looking to sell your company new steam traps, but the leaks they find and eliminate will more than offset the cost of a couple of replacement traps.

If you have any compressors in your plant, check the status of any recycle/blow off/antisurge valves. Most compressors require some type of an anti-surge valve on the discharge of the compressor which will automatically open if the compressor flow goes too low. Air compressors will usually just vent the discharge to atmosphere. Vapor (non-air) compressors will usually return the discharge back to the suction in order to keep the flow through the compressor above the minimum flow for the machine. If the anti-surge controller is poorly tuned or if the valve leaks, a tremendous amount of energy can be wasted continuously. If designed correctly, these valves should never be open in normal operation. If the anti-surge valves on your compressors are routinely allowing vapor (or air) to pass through them, investigate to see if changes cannot be implemented to close them.

Rule of Thumb: Any continuous waste stream is an excellent candidate for a money saving opportunity. Always keep an eye out for them.

Look for another tip next Friday.

 

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