Eliminate Steam Corrosion
My name is Kelly Paffel. I’m the technical manager for Inveno Engineering LLC. We’re located in Tampa, Florida. We are a domestic and international engineering firm focused on steam systems. Today I’m going to talk about eliminating steam system corrosion. Step one, deaerator operation.
Deaerator performance. A critical device in the steam system to prevent corrosion, of course in the boiler operation, but also in the steam system. The question I have for people, is the deaerator working correctly? Unfortunately, a percentage of deaerators are not meeting performance, and we’ll talk about that, specifically testing procedures.
Deaerator performance. High quality water required for boiler feed. Of course, non-condensable gasses eliminated. Steam quality for the process application. Non-condensable gasses go in with the steam, into the process, will suppress the temperature of steam called partial pressures. Deaerator performance is measured in units, parts per billion. International standard, 7 parts per billion.
There are two types of deaerators. One is a tray, agitation provided by spilling water over stacked plates or what we call trays. Also, steam is injected into the tray section to assist in the deaerator operation. Atomizer or spray is the other type, condensate and makeup water is sprayed through a set of spray nozzle, steam is injected to help in the process.
The first type is the deaerator tray design. Trays assist in the non-condensable gas elimination. Steam enters the tray section. So, in this picture here you have trays located in this section here, and you have steam coming in here to assist in the process. There’s a wire level here feeding all our storage for the boiler operation.
The other type of deaerator is a spray type deaerator. We can have two types. One is a fixed, or the other is a variable orifice design. Again, steam is used to assist in the process of eliminating non-condensable gasses.
Deaerator operation is scrubbing gas, of course, and steam. Has two actions, preheat the liquid for the boiler operation, increase the water temperature for gas elimination. Non-condensable gas elimination can be mechanical separation and diffusion of gas particles to the surrounding atmosphere.
All deaerators must vent non-condensable gasses. The percentage of steam for the operation is vented to ensure the removal of the gasses. So, in this picture here, non-condensable gasses are being vented with the gasses to ensure that we’re getting rid of the gasses out of the deaerator operation. The major question is, what is the correct amount of steam? How much steam should I be venting to ensure that I’m getting rid of the non-condensable gasses?
The old technology methods of testing deaerator performance. Steam venting, a small plume of steam 14 to 18 inches. A small plume is good, then a larger volume will be outstanding, correct? Negative unnecessary loss of energy, which can be substantial depending on the venting. It has no bearing of true deaerator performance, it just says, “I’m venting steam.” So in this operation, here you can see this [inaudible 00:04:16] deaerator operation. The question is, is this the correct amount of steam, or is this too much steam, or too little steam? We don’t know unless we dissolve oxygen as best as we can.
Another method is sulfite residual. A chemical test, easy to do on a daily basis, and should be done on a daily basis. Negatives, not a true measurement of non-condensable gas elimination, it just tells me I have sulfite residual. A deaerator can have sulfite residual, but they have the dissolve oxygen test. I’ve seen deaerators that have sulfite residual, and when we do the ASME test, they test out 300 parts per billion. Therefore, we must do the ASME test, which the ASME standard is PTC 12.3. You have to remove the sulfite for 48 hours prior to testing because we want to measure true deaerator performance, which is 7 parts per billion or lower. This should be accomplished every six months. Not a bad test to do. It’s not that difficult to do, and some plants do it monthly, but at least do it every six months. That will tell you the deaerator performance.
When conducting the dissolve oxygen test, then we can adjust the steam venting based on the dissolve oxygen test. Example: three parts per billion, then I can reduce the amount of venting, so I’m at three parts per billion, I can reduce the amount to venting. So, I don’t want to go over five parts per billion, and definitely not over seven parts per billion, but I do not want an energy loss here, unnecessary. If I get a reading of 20 parts per billion, venting should be increased because I know that will help assist in getting rid of the non-condensable gasses. The other thing that you can do is adjust the steam pressure. You have people say, “Well, the arrow should be operating at five PSI,” some people say, “Should be operating at eight PSI,” and other people say, “It should be operated at 12 PSI.” What is the correct pressure? The correct pressure is, I need to get below seven parts per billion. So, I can adjust pressure, I can adjust venting to make sure that I’m going to achieve a correct reading of seven parts per billion or lower.
On this deaerator test and the venting was reduced. A good amount of energy or dollars was accomplished. The other thing, is looking at visual inspection of the spray nozzles or springs and the trays, even looking at the internal tank system or components to make sure that we do not have oxygen pitting inside the deaerator, but I always like to do this on spray type deaerators or any spray, if I can get in there and get a good, so this is the atomization coming out here with the [inaudible 00:08:02], steam going through it because again, [inaudible 00:08:07]. With these, we have a deaerator that is not performance, and you can see that this is not a really great spray. It’s hitting the diffuser plate. We want to do, on sprays, is to get into those smaller particles available so the water can gain energy from steam and release the non-condensable gasses because of surface area. So, I always say visual inspection of the spray operation is a really good thing to do on a yearly basis.
Now the other method that we can talk about is on line dissolved oxygen testing, which is a great, great device to have on deaerators. There are several vendors, and they’re very, very accurate, ensures proper operation of the deaerator. So, these will give us some measurements here of dissolved oxygen. This one here is running at 0.1 PPB, which is outstanding. This one here is going through calibration, which is measuring 0. So, another device to help us to make sure that our deaerator is working correctly.
But anyway, Inveno Engineering, our approach, short term. Steam assessments, steam balance, steam performance, training, long term upgrades process. If you ever have questions, please contact us. Our email address is down here, or our website. Thank you for your time, have a great day.