Anti-surge and GT are critical applications and use prop. TMR PLC's.
You can do it with PLC's. But look out for long development cycles on a non-standard product.
get at least get a 1:1 redundant system.
Surge Control PLC should be real fast.
Using a PLC to control compressors is quite common in the natural gas
pipeline industry. This is done on both turbines and reciprocating engines.
I worked on a retrofit of a Solar turbine a few years ago. The "black box"
controller was removed and replaced with a PLC connected to all of the
associated I/O. Some of the field devices had to be replaced to be compatible with the PLC I/O. The original technical manual (which was very detailed) was used as a guide to write the ladder logic. There were PID loops for pressure, speed, surge, temperature control, etc. The rest of the logic was valve sequencing and alarming. Intellution was used as a HMI. I've only been involved in retrofits, but I'm pretty sure that Solar now offers a package with an Allen-Bradley PLC5 or Control Logix in it.
I've got a two-page write-up on compressor surge control. It's geared toward single loop controllers, but does a good job of describing the control theory. I can fax it to you if you like.
We are performing antisurge control functions using a Triconex Version 9 TMR PLC
on a three stage centrifugal compressor with two side loads that is used in
refrigeration service. The machine has an electric driver, so no speed control is needed, however, that module is also available if needed. I have seen the system keep the compressor out of surge in some rather unusual operator induced
situations, so it does the job quite well.
The whole package was provided by the Triconex shop in the Houston area. While I
realize that Triconex is not the cheapest, it does have the ability to change out the I/O cards without having to shut down the compressor. If long duration runtime is one of your criteria, then this is the way to go. It can also interface to a DCS system via Modbus RTU or to the Honeywell TDC-3000 via either Data Highway or UCN interfaces. Check them out at www.triconex.com
Calumet Lubricants - Shreveport Refinery.
Anti surge control and surge shutdown are two separate tasks. PLC's can perform both functions. Preferably a surge shutdown system should be implemented using hardware that is separate from the anti surge control system. The system including the surge arrest valve(s) must be very fast. This is especially important for an axial compressor compared to a centrifugal compressor. Axial compressors should have surge arrested within one surge cycle to prevent axial blade fatigue or possibly even complete separation of blade from shaft. Centrifugal compressors are a little more rugged.
A simplified anti surge control is basically a constraint control system where the constraint is the set point to a controller modulating a valve to prevent the compressor from entering the surge region. The constraint is a characterized surge curve (pressure vs flow). As long as you are far enough away from the constraint, the modulating valve remains closed. As the curve is approached by say pinching off the discharge of the compressor, the anti-surge controller will begin opening the valve to prevent the compressor from going into surge. The PLC type used should be able to service this loop quickly. A vendor of a dedicated antisurge controller claims updating anti surge calculations every 40 msec.A PLC that can perform these calcuations with this update time would do. Many PLCs including soft PLCs could perform anti surge control.
One of the more important tasks in implementing surge control is to obtain accurate surge data. In one application I was involved with, we had to surge the compressor at several discharge pressures to obtain the curve. The available curves were considered unreliable.
Reiterating what has been previously stated; Compressor surge control is a
very specific application. While it can be performed using a PLC various
factors such as; speed, redundancy, algorithm correctness, sensor
interface, etc. need to be very carefully reviewed. This is why companies
such as Compressor Controls, and Triconex have specialized in this area.
Our company, InFLOW, INC. has over twenty years experience in compressors
from a design, application, and operation perspective. We also provide
control system solutions using a variety of techniques including PLC's.
Please contact us if you would be interested in further discussions.
I know of one company that has done this quite successfully with Allen
Bradley PLC's. They are an OEM of our HMI software, and have considerable
expertise in running compressors at maximum efficiency. Some of the HMI
objects they put together in their package can attest to this. They have won
quite a few contracts against the bigger suppliers with their packaged
solution, recently the Toyota Plant in Kentucky (Largest Air Handling
requirements in North America). The company name is Centrifugal Equipment
Service Corporation. You can see an example of one of their systems on our
WWW site under Industry Profiles, Centrifugal Compressors. The page includes
a write up and link to their site. Good Luck.
Yes, and Yes. Our company Petrotech Inc. has successfully implemented hundreds of anti-surge control systems and gas turbine controls in PLC systems. Our first PLC gas turbine and compressor anti surge control system was commissioned in 1993. We have been implementing microprocessor based anti-surge control and gas turbine control since the 80's using our proprietary hardware.
We have also implemented pnuematic anti-surge control systems.
One thing is detecting a surge and then taking the corrective action, and another thing is preventing a surge and having the compressor running at its optimum performance. In both cases you can use a PLC or a dedicated controller, as long as the speed response is good enough. Typically it is required to run the preventive anti-surge algorithm in less than 40 mS, so
you have to take this into consideration when selecting the hardware.
However if you are talking about preventing (and I hope this is the case) a surge, the key issue is basically the engineering required to properly configure, start-up and tune the anti-surge algorithm. Unless you are going to develop the anti-surge algorithm by yourself, the decision about the hardware platform to be used will depend basically on the company you selected to supply the anti-surge controller system (including engineering and support services), since typically these companies have their solutions already implemented on specific platforms (most of them on dedicated controllers, some on PLCs).