PM spiking and PS-11 Testing for PM Monitor Calibrations

Transcription

1 PM spiking and PS-11 Testing for PM Monitor Calibrations Robert W. Baxter, B3 Systems, Inc., Raleigh, NC Principal Contact: Robert W. Baxter, B3 Systems, Inc., 3208 Spottswood Street, Suite 106, Raleigh, NC 27615, phone , fax ABSTRACT During the previous CEMS conference we presented a paper on some of our early experiences with utilizing our method of spiking particulate matter (PM) to elevate the PM concentration in the off gases while performing calibration efforts on PM continuous emission monitoring systems (PM CEMS) calibration. Since 2011, this method has been successfully used on over 15 applications, on both wet and dry stack conditions. The information and knowledge gained has been tremendous. Not only about our PM spiking operation but also the operation of PM CEMS. This presentation will be a case study of these experiences and what we have learned. 1. BACKGROUND The number of Particulate Matter Continuous Emission Monitoring Systems (PM CEMS) applications in the United States is growing as well as the experience level of users with PM CEMS. To support this market, B3 Systems developed and patented a PM Spiking method to assist facilities in the calibration and quality assurance (QA) process for Performance Specification 11 (PS11). PS11 defines the requirements for PM CEMS requirements applications under the United States Environmental Protection Agency (USEPA). In the CEM 2011 conference B3 Systems provided a case study regarding our early learning experiences taking the PM spiking system into the field. By the time this paper is presented at the CEM 2014 conference, B3 Systems will have performed PM Spiking in over twenty PS11 programs/units for establishing the initial calibration curves as well as the response correlation audits (RCA). B3 Systems has always filled a niche in the environmental testing and monitoring business. But the PM spiking service has allowed us to use our experience and knowledge from other industries, processes and regulatory rules. Combining that knowledge with seeing so many different PM CEMS applications in a short amount of time has placed us in a very unique position and view of the PM CEMS market. 2. EXPERIENCE TO DATE The following table provides a summary of the application B3 Systems has been involved with to date, all with successful results. Dry Stacks 16 Wet Stacks 4 Total 20

2 2.1. Dry Stack Gases Dry stacks gas applications, non-condensing waters droplets, are the ideal situation for PM Spiking. In most cases we inject the native PM into the inlet of the induced draft (ID) fan. The fan the handles and distributes the PM in the same manner as any system upset. Dry gas applications provide the most representative situation to monitoring a real-plant upset because the fan defines the PM distribution and stratification in the system Wet Stack Gases The wet applications, ones that have water droplets present, represent the more difficult PM spiking applications. The PM has to be injected downstream of all scrubbing devices just prior to the stack. We have found that injecting from the top of the duct provides the best results. Depending on the configuration of the scrubber outlets the injection locations can be feet above the ground level. We have had injection locations as high as 230 feet above the ground. This is further complicated by the fact that pneumatic transport of solids is limited to about 180 feet in vertical rise. Therefore these applications require booster stations. There is always a question as to how well the PM is distributed in wet stack gas applications. But our experience is that PM is always stratified, it is more about more much or how little it is stratified. But independent of those questions, PM spiking has been used to successfully conduct RCA's on initial curve that were not created using PM spiking. Therefore this indicates validity in the approach and technique. 3. QUESTIONS ABOUT PM SPIKING Since the use of PM spiking is so new there are a lot about how it works, will it work and is it allowed. The following is a short list of questions being asked by others. What is the particle size distribution? Is the spiked PM representative of normal operations? Does pre-screening the PM bias the results? How much small PM (<2-5 microns) is lost during screening? What is the mixing/distribution of the spiked PM? Is PM Spiking representative of a process upset? Is PM Spiking representative versus detuning the scrubber? Do PM CEMS really work? The following sections will try to address some of these questions What Is The Particle Size Distribution? The short answer is Whatever your normal PM distribution is.. But during more detailed discussions it becomes apparent that this question covers a much larger area, but generally comes up based on normal plant operation or in reference to the fact that B3 Systems now pre-screens the spiking material taken directly from the baghouse or ESP hoppers. As far as the spiked PM particle size distribution being representative to normal operations, the question appears to be worded incorrectly. The focus should not be on spiking material, it should be on what is normal versus abnormal for the facility.

3 A plant operating at normal conditions, usually means low PM, e.g., no leaks in the baghouse or the ESP operating in top condition. As soon as the PM levels start to elevate, it is not normal any longer. The change in PM is probably due to an abnormal situation or condition in the process or air pollution control device. Personal experience and discussions with facilities have lead to the conclusion that abnormal operations are not particle size selective. Therefore this question is not really answerable as it is being asked. You first understand the characteristics of the facility under different conditions before you can define normal for each of the specific conditions. This PM representative question also surrounds the pre-screening operation of the spiked material. The question seems to come from people who are more on the academic side versus the implementation side of PS11 programs. After having the same issues on the first few programs with larger particles getting into the system and causing system problems, a process of pre-screening the spiked material was implemented. B3 Systems now pre-screens the native PM to remove oversized particles (>250 microns). This process only removes particles which can cause problems during the PS11 testing program and large particles which would probably fall out in the gas stream and never make it to the PM CEMS unit anyway. The majority of PM seen so far has a normal distribution of less than 50 microns, therefore particles greater than 250 microns as not normal. Therefore we do not think this affects the results of the testing How Much Small PM (<2-5 microns) Is Lost During Screening? This question seems to come from the equipment providers since they really want the minutely small PM, especially 1 micron and less, since it floats through the system easier than the larger particles. On the average the overall losses from the screening operation, which included extremely small fines and human spillage, is less than 0.5%. Spiking materials such as fly ash, raw meal, etc from facilities are completely different in both their particle size distribution to the way they handle. Therefore the pre-screening process is used to obtain a lot of additional information that helps the field spiking operations What Is The Mixing/Distribution Of The Spiked PM? Dry scrubber systems have not shown any issues from spiked PM. For these systems the PM is normally injected into the inlet of the induced draft (ID) fan. Since the fan is the best mixer in the system and defines the distribution of the discharge gases, velocities and PM. Therefore the ID fan defines normal distribution for the system. Spiking into wet scrubber systems provides a different challenge since the PM is injected down-stream of the fan. B3 Systems has been involved with three (3) programs with wet scrubbers and each new program provides insight into how these systems should be handled. Consistency and repeatability are critical to these programs, especially at this stage of understanding. Ultimately the questions of PM mixing and distribution are related to PM stratification. The only PM stratification data seen to date is from one wet scrubber system. This data shows that the system is more stratified with spiked PM versus baseline operations. However it is not known if the spiked PM is more stratified or if the additional PM just amplifies the stratification. No known stratification data is available during plant upset conditions, therefore it is impossible to say if the spiked PM data is representative of plant conditions with elevated PM. But it should be pointed out that the bigger issue for meeting the requirements of PS11 is being able to repeat conditions used for the initial curve.

4 3.4. Is PM Spiking Representative (Of A Process Upset)? This question is really two questions in one: 1. Is the spiked PM producing representative results that can be used to calibrate the PM CEMS? 2. Is the spiked PM representative of process conditions? Starting with question #2 first, the technically correct answer is that nobody really knows. As discussed previously in this paper, elevated PM is abnormal and no known stratification or particle size data is available taken under these conditions. As for question #1, if there is no basis for answering question #2 then #1 can not be answered directly. However an indirect indication can be obtained from Figure 1. Figure 1: Extended Curve with PM Spiking In Figure 1, the square data points were generated from several tests during process upset conditions (e.g., baghouse leaks). However the facility needed to extend their curve further and chose to use PM spiking to obtain the elevated PM test data, the triangle data points. Even though this data has all of the variations associated with process / field data, you can see that the spiked PM results are a nature extension for both the process baseline and process upset data points. Another point of view for this question is whether the particle size distribution and mixing / stratification is representative when an APC is defeated, detuned or by-passed? If the APC is defeated, detuned, or by-passed the stack gases can still result in stratified conditions based on the mechanism or method used. By-passing a scrubber usually results in two different gas temperatures trying to be mixed and the PM is mostly in one source. It is our experience that it will almost be certain that the final stream will be stratified due to different gas densities. If a part of the PM control device is defeated, then the majority of the PM will be coming from one area within the system. This can also result in stratified conditions for the PM CEMS.

5 3.5. Do PM CEMS Really Work? The question that comes up the most, especially from facilities who are just starting to look at them. Of course they want to hear that they do not work, but our experience shows that they do. Figure 2 below is a summary of block hour averages of the PM Spiking rates (lbs/hr) versus the PM CEMS output. Nobody should ever try and plot a mass rate vs a concentration. There are just too many undefined variables (e.g., gas flow, background PM, etc) PM CEMS Output Figure 2: PM Spiking versus PM CEMS Output PM Spiking Rate (lbs/hr) But this facility operated with a very low and constant back PM concentration and was very consistent in their stack gas flow rates. We have seen this type of response at many of the plants we work at. Therefore we have to say that PM CEMS do work. 4. WHAT WE HAVE LEARNED Based on our experience, PM CEMS do work and PM Spiking is a valid method of conducting your PM CEMS initial correlation and RCA tests. But a successful program is more than just installing a PM CEMS unit and generating some data. Careful planning is required from initiation choice of the technology to the testing. Below is a brief list of what we consider to be the key items to a successful PS11 program or at least provides a strong basis for a successful program. Choose the right PM CEMS technology Choose a representative monitoring location Get a wide spread in the data for the initial curve PM control device maintenance Setup your testing conditions Document all of your testing conditions

6 The following sections will provide a brief summary and explanation of the items listed above Choose The Right Technology This paper will not get into any of the specifications of existing PM CEMS technologies, however we feel that choosing the right technology is a key first step in a successful program. The right technology is more than just a detector, it is an instrument that fits into a facility's structure and work flow. It is something that works with less maintenance than the other options and personnel are comfortable working on it and maintaining it. The right technology can meet the demands of the stack conditions and PM characteristics and probably comes with a good support team. The right technology is not driven by cost, but if everything else is equal then cost can be the tie-breaker. In some applications several technologies may work equally as well. But the right technology is the one that your maintenance personnel are comfortable with, will maintain it and does not generate maintenance issues for them Representative Monitoring Location Regardless of the technology chosen, it must be placed is a location that is representative of overall stack concentration. If monitoring systems are being installed as part of an over construction project, get involved. There is a good chance that construction personnel do not have the experience or knowledge required to mount the PM sensor in a representative location. Although B3 Systems has not taken part of locating the representative location, it is known that some facilities have conducted stratification testing, similar to a CEMS stratification testing, to help identify the best monitoring location for the PM CEMS. In other cases good process knowledge may be more than adequate. We should not have to say it here but we will. Just because a port is available does not make it a representative monitoring location Data Spread For Initial Calibration Curve A wide range in the data set used for the initial calibration curve helps in many areas. All facilities have a cycle or noise level for everything parameter in the facility. This is also true to PM emissions (e.g., baghouse cleaning vs filtering only). Therefore spreading the data as far as possible outside the natural process variations or noise level results in a better correlation for the initial calibration curve. It also means less chance of tripping the 125% limit and having to retest. Another benefit of spreading the data in the initial curve will probably not be realized for several years. But the data used in the RCA phase of a PS11 application must not fall within the data used to establish the initial calibration curve. Therefore extending the data set, both high and low, for the initial curve makes it easier to get valid data points for the RCA later.

7 4.4. Define Testing Conditions The title for this section is very general but it encompasses a much bigger and important part of your PS11 program. Details on this section are very site-specific and could be a short workshop within themselves. This paper will only address the broader topics of this subject. The key words to remember for this section are: consistency repeatability These two words are very important to almost every aspect of your program. There needs to be consistency and repeatability in: the reference method testing stack gas flow stack gas temperature stack gas PM concentration Therefore we recommend approaching this similar to a hazardous waste trial burn. Know what conditions you can obtain, hold and repeat within the process. Remember that your PS CEM is being correlated on concentration versus the reference method therefore maximum flow rates are not necessary. In fact it is more important to have process conditions that can be held steady for the duration of testing. This includes not just gas flow rate and temperature, but also PM concentration. Holding these steady normally results in a better correlation between the single point PM CEMS and the reference method that traverses Document All Testing Conditions With all of the above taken care of, the final piece to the puzzle is documenting all of the conditions used in setting the initial calibration curve. This will be most important when it comes time to conduct the RCA on your PM CEMS. Referring back to the key words identified in the previous section, the same is true for the RCA except that the target should be the same conditions used to establish the initial calibration curve. The gas in the duct and stack is a dynamic process that is constantly changing. Therefore getting it as close to original conditions will help the RCA results. 5. BENEFITS OF PM SPIKING The are numerous ways to elevate the PM concentration in the stack gases. However PM Spiking provides the great level of consistency, repeatability, and control 6. WHERE WE ARE GOING B3 Systems has been contacted by several PM CEMS manufacturers and industry users groups about developing an alternative approach to help stream-line the PM CEMS calibration and QA processes. This work is still in the very early stages of development, but based on the data we have seen from full-scale plant operations we are convinced that the process can be simplified. Hopefully by the next CEM conference we can provide an update on this work.