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1 Comparison Tests and Product Validation Testing of Cambridge Environmental Technologies Electrostatic Precipitators for Wood-Fired Boiler Applications April 2012 Dr. Grace Pokoo-Aikins Cambridge Environmental Technologies, P.O. Box 399 USA Phone: (410) ext Main Line: (410) Abstract Cambridge Environmental Technologies (CET) Performance Validation Testing (PVT) unit was installed on a slip stream exiting a wood-fired boiler at a lumber yard in Maryland from September 2011 through March Tests were conducted in order to understand various aspects of the system, including three main goals: 1. To understand how the CET Kinetic Electrostatic Precipitator (KESP; or belt unit) performs when cleaning wood ash particulate. 2. To understand how the CET plate Electrostatic Precipitator (plate ESP; or plate unit) performs when cleaning wood ash particulate. 3. To compare the performance of the CET KESP with a traditional plate ESP unit. Results revealed that the belt unit consistently collected particulate with greater than 90% collection efficiency while the plate unit collection performance was less consistent and displayed huge swings in collection performance. The belt unit out-performed the plate unit in terms of collection at temperatures below and up to 350 o F. Collection performance of both units was comparable at temperatures above 350 o F, but the belt unit once again displayed the potential to out-perform the plate unit. The CET KESP has demonstrated superior performance over a plate-type ESP in cleaning the gas stream from a wood-fired boiler. Since system conditions were the same during the test period, differences in performance are attributed primarily to differences in design between the belt and plate units. There were two major design differences. The first was the introduction of increased surface area through the use of mesh belts 1

2 instead of traditional plates. The second was an automated contact cleaning system located in the vicinity of the hopper, instead of traditional rapper, for reduced re-entrainment. The performance of the CET KESP unit can be further enhanced by selecting belts with different specifications and by tuning the cleaning system to the application. Further enhancements of the KESP include the use of an optional refined polishing system (RPS) on the back end of the KESP. The RPS is a continuously cleaning filtration system that uses a fine mesh screen to capture particulates leaving the KESP. Introduction Cambridge Environmental Technologies (CET) conducted performance validation tests of two electrostatic precipitator (ESP) designs, a traditional plate unit and a new type of belt unit called the Kinetic Electrostatic Precipitator (KESP). A single outer frame and test assembly was used with two interchangeable inner frames. One inner frame contained the plate unit while the other inner frame contained the KESP unit. The ESP test system was installed downstream of a 500 Hp Hurst wood-fired, fire-tube boiler to capture wood ash particulates. Flowrates for the boiler system were estimated at approximately 10,000 acfm. A slip stream of this larger flowrate was drawn into the CET system through the use of an induced draft fan. The electrostatic precipitator system was installed in September 2011 and uninstalled in April Data was collected from September 20, 2011 until March 13, Performance of the belt and plate units was monitored and logged manually during the tuning period when the two units were conditioned to the air stream. Opacity readings, data from the TR set, outlet temperature, pressure, and velocity were logged from January 4 until February 2, Additional instruments and sensors for measuring conditions at the inlet were installed and used to record data from February 17, 2012 until testing ended in March Data collected during the test period revealed valuable information about the performance of the two types of electrostatic precipitators. Results revealed the capabilities of the two types of units, including 2

3 strengths as well as opportunities for improvements. The test results also demonstrated that the KESP has design advantages over the traditional plate ESP. Methods of Testing Several methods were used to test the CET electrostatic precipitator installed downstream of a woodfired boiler and to gather data about the unit s performance. Performance validation testing involved conducting filter tests, monitoring opacity, and recording temperature, pressure, and velocity. Filter Tests Short duration and long duration filter tests were conducted. Short duration tests were one hour long tests conducted a minimum of three times for each type of unit (plate unit or belt unit). Short duration testing allowed for more data points to be collected in a given test day but it had one major drawback. With the shorter runs, less particulate was collected compared to longer runs. Thus any particulate losses affected the results more markedly and led to larger margins of error. Long duration tests lasted for more than one hour (from 2 hours to 5 hours). Considerably more particulate was collected during long duration tests and thus minor losses of particulate had less of an impact on the results. Filter testing involved inserting clean, pre-weighed and pre-dried Grade AE fiberglass filters into 3 inch ports (one at the inlet and another at the outlet) in the duct work and leaving the filters inserted for the duration of the test run. The location of the ports was based on EPA method 1A for Sample and Traverses for Stationary Sources with Small Stacks or Ducts. The fiberglass filters were mounted inside custom designed stainless steel and aluminum filter holders. Prior to testing, the clean filters were dried to a constant weight at 350 o F. The dried filters were weighed, labeled and stored in aluminum foil pans and covered with an aluminum foil sheet to prevent contamination. There were two filter holders, one for the inlet port and one for the outlet port. Before each test, the filters were loaded (1 filter each) into filter holders and then inserted into the test ports. At the end of each test run, the 3

4 filter holders were removed from the ports. Each filter was removed from its filter holder and then placed back in the same aluminum pan used for the pre-weighing. The filters were taken back to the CET lab where they were weighed, dried to a constant weight, and weighed again. An A&D HR-200-C analytical balance was used to weigh the filters and toaster ovens were used to dry the filters. and outlet particulate masses were used to calculate the final collection efficiencies. Opacity Opacity was monitored using Datatest Industries Model DT109D Dual Pass Opacity Measurement Systems. One opacity monitor was installed in the ductwork leading to the inlet of the ESP system, and another opacity monitor was installed in the ductwork exiting the precipitator. In practice, opacity monitors are typically only installed on either the outlet ductwork or on the outlet stack. Two opacity monitors (one at the inlet and another at the outlet) were used in order to obtain data about the ESPs performance. By measuring the difference in opacity between the inlet and outlet ducts, it was possible to compare the performance of the CET KESP with the performance of the CET plate ESP. Opacity was recorded as percentage values. The opacity data was used to calculate collection efficiency based on opacity. Efficiency based on particulate mass collected is the true collection efficiency. The collection efficiency based on opacity was not a true collection efficiency but an apparent collection efficiency. Since the conditions of the two systems being tested were kept as uniform as possible the opacity data could be used to compare the performance of the two CET ESP units., Pressure and was measured using a Type K thermocouple probe (one at the inlet and one at the outlet). Each probe traversed the duct at the appropriate location in accordance with EPA method 1A. The temperature probes were mounted statically at the center line and center point in the duct. signals were transmitted to the data logger through an Omega Smart Transmitter (TX13) at the inlet and through a Jenco DPT-B5 Pressure/ Transmitter Display 4

5 from Apex Instruments at the outlet. Pressure was measured at the same location as the temperature using a Type S Pitot tube (4PT-2-TF) from Apex Instruments (at the outlet until 3/2/12 and then at the inlet until 3/13/12) and a Dwyer Instruments Series 160 Stainless Steel Pitot Tube (at the outlet from 3/2/12 until 3/13/12). The pressure signals were transmitted to the data logger using a DPT-B5 (Apex Instruments) differential transmitter at the outlet and an Omega differential pressure transmitter (PX409-10WDWU) at the inlet. Pressure data were logged and converted to velocity data, which were also logged. Results Filter Tests temperatures, outlet temperatures, and outlet velocities were collected for all runs conducted during the short-duration and long-duration filter tests. Table 1 summarizes the results of the filter test data. Based on the results, the belt unit outperformed the plate unit at inlet temperatures below 300 o F. When the inlet temperature was less than 270 o F, the belt unit performed significantly better (96.7, 95, 91.3 and 95.0% collection efficiency) than the plate unit (6% collection efficiency). Between temperatures of 270 o F and 300 o F, the belt unit filter tests resulted in collection efficiencies of 98.5 and 94.1% (2/23/12 & 2/28/12) while the plate unit filters tests had collection efficiencies of 72.4 and 90.6% (1/19/12 & 2/16/12). On 2/16/12 and 2/28/12, the inlet and outlet temperatures and the inlet and outlet velocities for the belt unit closely matched the plate unit. The belt unit performed at 94.1% collection efficiency while the plate unit performed at 90.6% collection efficiency. At inlet temperatures above 300 o F, the belt unit displayed the potential for superior performance (92.1% collection efficiency on 2/29/12 and 97.9% collection efficiency on 1/6/12) to the plate unit (93.4% collection efficiency on 2/15/12). At inlet temperatures greater than 350 o F, the belt unit once again displayed the potential to outperform (94.2% collection efficiency on 1/26/12) the plate unit (72.3% collection efficiency on 3/9/12). At even higher temperatures (greater than 400 o F), the plate unit displayed the potential to perform well (96.6% collection efficiency). The belt unit did not experience process temperatures above 360 o F during the filter tests while the plate unit reached temperatures in excess of 400 o F. More tests 5

6 are needed in order to compare the performance of the belt and plate units at temperatures above 400 o F. Table 1. Comparison of filter test results based on inlet temperature Date Unit Average Collection Efficiency Average Temp Average Temp Average Average 2/21/12 belt /20/12 belt /1/12 belt /20/12 belt /8/12 plate /23/12 belt /16/12 plate /19/12 plate /28/12 belt /6/12 belt /15/12 plate /29/12 belt /26/12 belt /9/12 plate /13/12 plate Daily Run Data Daily run data is available for certain dates between December 15, 2011 and March 13, By sorting the data based on outlet temperature, it was possible to compare the results from the plate unit with the results from the belt unit. In the first few sets of data from the daily runs, the results compared the performance of the units when the air running through the systems was relatively cool (temperatures between approximately 40 and 75 o F). The data was grouped based on an attempt to match similar conditions. Both units performed at high efficiencies (greater than 90% apparent efficiency based on 6

7 opacity). Cambridge Environmental Technologies In comparable conditions, the plate unit performed poorer (95% and 96.7% apparent efficiency) than the belt unit (99-100% apparent efficiency). At temperatures where significant condensation is expected to be present in the system, the belt unit excels. The performance of the plate unit, although less effective than the belt unit, was much better than expected. The next increment of outlet temperatures for which data was compared is outlet temperatures ranging between 90 and 105 o F. Corresponding inlet temperatures ranged from 211 to 276 o F. Once again, in this temperature range, the units were likely to experience some condensation. Condensation can lead to sticky ash that would be difficult to remove from collection electrodes with traditional rapping as used in the plate unit. In this temperature range, the belt unit once again out-performed the plate unit. If the moist environment was the reason that the belt unit performed better than the plate unit, it may be because the KESP has moving belts and a contact cleaning system while the plate ESP uses a rapper. The traditional plate rapper may not be sufficient to dislodge sticky material from the plates. When considering all the data in this temperature range, belt performance ranged from 96% to 100% apparent efficiency while the plate performance ranged from 86% to 95% apparent efficiency based on opacity. It is important to note that in this temperature range, there were significant differences in flowrates. However, by comparing data at similar conditions it became clear that the belt unit did significantly better than the plate unit. When considering outlet temperatures greater than 110 o F but less than 125 o F, it was expected that the rise in outlet temperature would correspond with an increase in the inlet temperatures and an improvement in the performance of the plate unit since drier, less sticky particulate was expected to be found in the system. On 2/29/12, the belt unit captured particulate with 100% apparent efficiency compared with 87% efficiency for the plate unit (2/16/12) at similar inlet temperature, and inlet and outlet flowrates. Comparing results at similar outlet flowrates from 2/3/12 (belt) and 2/14/12-2/15/12 (plate), the belt unit once again performed at high efficiency while the plate unit performed at 94% efficiency. Data for 3/1/12 (belt unit) and 3/7/12 (plate unit) were also compared. At these conditions, both units performed at 98%. Data from 3/1/12 for the belt unit is somewhat comparable to data for 3/4/12 for the plate unit and the belt unit performed at 98% while the plate unit performed at 100%. The plate unit has not otherwise performed at such high collection efficiency. The most likely 7

8 explanation for this result is that the boiler was being operated differently (larger inlet loadings for the plate unit) than during other runs when data was being collected. The boiler was observed to have issues around that time (3/4/12-3/7/12). Also, while other variables are comparable, the inlet velocity for the plate unit is much higher than for the belt unit. For the plate unit, the relatively high inlet velocities may have served to dislodge particulate that had adhered to the plates. temperatures between 110 and 125 o F are presented in Table 2. Data for Table 2. Comparing Plate and Belt Performance at s between 110 o F and 125 o F Date(s) Unit Type Instantaneous Opacity CE% 2/14-2/15/12 Plate % 3/7/12 Plate % 2/29/12 Belt % 3/4/12 Plate % 2/22/12 Belt % 2/3/12 Belt NA NA % 3/1/12 Belt % 2/16/12 Plate % For outlet temperatures above 130 and below 145 o F, the plate unit had improved performance with increasing temperature. However, the performance of the belt unit once again exceeded that of the plate unit. The plate unit performance was between 93% and 100% while the belt unit performed at 100% efficiency. The data for this temperature range are presented in Table 3. 8

9 Table 3. Comparing Plate and Belt Performance at s between 130 o F and 145 o F Date(s) Unit Type 2/15/12 Plate % Instantaneous Opacity CE% 3/2/12 Belt % 3/8/12 Plate % 3/8/12 Plate % At outlet temperatures in excess of 150 o F, the inlet temperatures were observed to be near or in excess of 350 o F ( o F). At these higher temperatures, the plate and belt units performed comparably. On 1/6/12, the plate unit performed at 97% apparent efficiency while the belt unit performed at 96% and 97% efficiency on 2/23/12-2/24/12 and 1/8/12 respectively. Data for temperatures between 150 and 160 o F are presented intable 4. Table 4. Comparing Plate and Belt Performance at s between 150 o F and 160 o F Unit Instantaneous Date(s) Type Opacity CE% 1/6/12 Plate NA NA 97.20% 2/23/12-2/24/12 Belt % 1/8/12 Belt NA NA 96.70% At even higher outlet temperatures, the plate unit continued to perform well. temperatures in the range of o F (see Table 5) corresponded to inlet temperatures between o F. On 1/13/12 the plate unit performed at 96% efficiency and 97% on 1/4/12 while on 3/10/12, the plate unit 9

10 performed at 100% efficiency while the belt unit performed at 98% efficiency. These results indicated that the two units are capable of comparable performance at higher temperatures. There may be conditions where one unit can outperform the other at higher temperatures, but further testing would be required to determine those conditions. Table 5. Comparing Plate and Belt Performance at s between 170 o F and 180 o F Date(s) Unit Type Instantaneous Opacity CE% 1/13/12 Plate NA NA 95.60% 3/10/12 Plate % 1/7/12 Belt NA NA 97.60% 1/4/12 Plate NA NA 96.70% Finally, when comparing results for outlet temperatures in excess of 180 o F (see Table 6), it was found that both units continued to perform well and comparably. At outlet temperatures above 180 o F, inlet temperatures above 350 o F were observed. At these conditions, the performance of the plate unit ranged from % efficiency with several data points above 99%. The belt unit performed at 99.7% efficiency. Both units have demonstrated good performance at inlet temperatures likely between 370 and 400 o F. 10

11 Table 6. Comparing Plate and Belt Performance at s above 180 o F Date(s) Unit Type Cambridge Environmental Technologies Instantaneous Opacity CE% 1/26/12 Belt NA NA 99.70% 12/17/11 Plate NA NA 99.00% 3/3/12 Plate % 3/2/12 Plate % 1/5/12 Plate NA NA 96.90% 12/16/11 Plate NA NA 99.30% 3/9/2012 Plate % Discussion Particles behave differently at different temperatures. Figure 1 illustrates the temperature/resistivity relationship. For every type of particulate, there exists a resistivity curve. The curve is such that resistivity increases with temperature up to a maximum temperature/resistivity, beyond which, resistivity decreases with increasing temperature. The results and knowledge about resistivity 1 reveal that the collection efficiency for both units will likely have two maximum peaks corresponding to the areas of medium resistivity on the resistivity curves for wood ash. There will also likely be a trough (low collection efficiency) corresponding to the region of high resistivity on the resistivity curve between the two peaks (high collection efficiency). Therefore, efficiency would be at the lowest in the regions of low resistivity, increase to a peak in the range of medium resistivity and before the areas of high resistivity, either flat line or drop to a trough in the regions of high resistivity and increase again to a peak as the resistivity curve comes back down. To aid in visualizing the results, the data was sorted based on inlet temperature and graphed for both the KESP and the Plate ESP. Some data was interpolated or estimated based on outlet temperature. 11

12 Collection Efficiency (%) Cambridge Environmental Technologies Effects of on Particle Resistivity and Collection Efficiency High Resitivity/Collection Efficiency Low Resistivity/Collection Efficiency Resistivity Collection Efficiency Figure 1. Relationship between temperature, resistivity and collection efficiency. 100 Filter Test Results Summary ( o F) KESP Plate ESP Figure 2. Summary of Filter Test Results In the results for the filter tests (Figure 2), there are noticeable peaks and troughs (more so for the plate unit than for the KESP). This chart depicts that the belt unit performed consistently above 90% efficiency. For the given data the belt unit performed best at about 270 o F and near 310 o F. The plate 12

13 Apparent Collection Efficiency (%) Cambridge Environmental Technologies unit performed well at about 290 o F and at temperatures above 315 o F. The region of high resistivity is likely between 270 o F and 310 o F for the belt unit and 290 o F and 315 o F for the plate unit (more likely between 294 and 297 o F). Beyond 315 o F, the collection efficiency showed an upward trend for both units. Daily Run Results Summary 100.0% 98.0% 96.0% 94.0% 92.0% 90.0% 88.0% 86.0% ( o F) KESP Plate ESP Figure 3. Summary of Daily Run Results Results for the daily run tests (Figure 3) also reveal noticeable peaks and troughs. The performance of the KESP seems to be independent of resistivity. In regions where the temperatures were near 212 o F (less than 250 o F), there may have been some condensation in the units but at temperatures approaching 300 o F, the condensation may be minimal and the troughs for the plate unit may be attributable to high resistivity. When looking at the daily run results for the plate ESP, the region of high resistivity seems broader than for the filter tests and is likely between 270 o F and 320 o F (near 290 o F). There are three troughs (one near 210 o F, another near 250 o F and one near 290 o F). It is unclear why there are multiple troughs for the plate ESP daily run data. The troughs near 210 o F and 250 o F are likely due to high levels of moist particulate in the plate unit. The region near 290 o F is believed to be a region of sensitivity because it is near a zone where the particulate transitions from medium resistivity to high 13

14 resistivity. Once again, the belt unit performance was consistent in spite of changes in resistivity of the ash. Again, at temperatures beyond 320 o F, both the KESP and the plate ESP show the potential for high collection efficiencies. Conclusions Filter tests and opacity monitor readings were sufficient to obtain reliable results. Filter tests and opacity readings were used to verify the performance of the system. The opacity readings alone may have been sufficient, filter tests were used as an extra measure to check system performance. Results indicate that under the given conditions, the CET KESP outperformed the plate ESP at temperatures below 350 o F. At temperatures above 350 o F, the KESP unit was comparable in performance but demonstrated the potential to outperform the plate unit. The superior performance can be attributed to either the increased surface area of the collection electrodes resulting from the use of mesh belts, reduced re-entrainment due to the self-cleaning mechanisms outside of the air stream, or a combination of both of these elements. At lower temperatures, the superior performance is attributed to the automatic contact cleaning system outside of the air stream. At higher temperatures, the results from these tests do not reveal which of the two mechanisms (cleaning system or increased surface area) is the major contributor to the improved performance. In either case, the KESP unit is a technology with numerous possibilities for enhancing the performance of pollution control through careful tuning. Performance enhancing measures include using different belt specifications and modifying the cleaning the system. Another possibility to further enhance the KESP unit includes the addition of an optional Refined Polishing System (RPS) on the back end of the KESP. Use of an RSP provides possibilities for utilizing sorbent control measures (i.e. sorbent coated filters on the RPS). The CET KESP unit has strong potential for advancing and improving decades-old precipitator technology. References 1. Mastropietro, R. A. (2004). Particulate control for biomass fired boilers. Presented at the 9 th International Symposium of Electrostatic Precipitation, South Africa, May,