# A Report on the Impact of Pellet Fuel Ash

Content on the Particulate Emission

Performance of Five Pellet Heaters

Prepared for the Hearth Patio and Barbecue Association (HPBA)

By: Robert Ferguson Ferguson, Andors & Company

February 15, 20112 Background

Many of the EPA certified pellet heaters were tested using pellets with very low ash content (< 0.5%). These pellets are made fr om softwood feed stock and are produced in the Pacific Northwest. These pellets are commonly available for the testing laboratory that has conducted much of the pe llet heater certification testing.

Pellets that are most commonly available in other areas of the country where pellet heaters are popular are generally hardwood or mixed wood and have higher ash content (>1%).

There was supposition that higher ash fuels woul d result in higher particulate emissions. This was based on observations made by pelle t heater manufacturers when they tested other fuel types (corn, grains, hulls, etc.) that were known to have higher ash content than premium wood pellets.

There was almost no data directly comparing the particulate emissions from low and high ash wood pellet fuels in the same h eater using the same test method.

There was concern over the impacts on Best Demonstrated Technology (BDT) since different pellets might produce different re sults, even when the burn settings are optimized. This concern expands further when other fuel types ar e considered (corn, grain, hulls, pits, switch grass, etc.) By only considering the certified pellet heater database, where very low ash softwood pellet fuel was used almost exclusively, the determination of BDT will most certainly be skewed toward a lower emission value than should be considered as representative of na tionwide pellet heater performance, even for the best performing heater models.

Data Gathering

HPBA has been working for the past six months to obtain data that will shed some light on this issue. Some direct comparison test ing has been conducted, both in manufacturer

labs and at one EPA accredited lab.

The five pellet heaters that were tested to obtain this data represent main stream pellet room or space heater technology and cover the ty pical range in terms of heating capacity.

All five heaters fell within an EPA lis ted heat output range from around 7000 BTU/hour at the low burn rate settings to aroun d 35,000 BTU/hour at th e highest setting.

We appreciate the cooperation and support of the manufacturers and the test laboratory that participated in this effort to gather important data. The identities of the

manufacturers and heater models as well as the test lab have been masked for the purposes of this study.3 The data that has been gathered for this re port includes test results from more than one test method. The testing for the results la beled “ASTM” utilized what is now ASTM E2779, the new pellet heater opera ting test protocol (that in cludes an integrated burn cycle covering the full range of operation of the heater) in conjunction with ASTM E2515 for measuring particulates using a diluti on tunnel. It should be noted that ASTM E2515 and ASTM E2779 report emission values “as measured”. The results labeled “EPA” are the EPA certification weighted average emission rates for the heaters. If the emissions during certification te sting were measured using EPA Method 5G-1 or 5G-3,

the results in the “EPA” column are values adjusted to Method 5H equivalents according to current EPA requirements. The results labeled “PM” are indi vidual Method 28 burn rate category emission results but are reported as the “as measured” EPA Method 5G-3 values. The pellet moisture and ash valu es were determined using ASTM E871 and ASTM D1102 respectively. Ash and moistu re determinations were conducted by qualified third party testing labs. The data are shown in the following tables.

Table 1 shows the results of testing from three different pellet heaters using lower and higher ash fuels with a direct comparison of measured emission rates as well as listing the

EPA certification emission rate for each heater.

Table 14 Table 2 shows the results of testing on two additi onal pellet heaters. These heaters were tested for EPA certification using low ash pe llet fuel. In addi tion, two individual burn rate category tests per EPA Method 28 we re repeated using higher ash fuel.

Table 25 In addition, the results are also presented in the following charts.

Chart 1 shows the ASTM E2779 average emissi ons and the EPA certification emission value for each of the three pell et heaters from Table 1, plotte d versus the pellet fuel ash

content.

Chart 1

Pellet Ash Content Effect on PM Emission Rate 3 Pellet Heaters (A, B & C)

0.0 1.0 2.0 3.0 4.0 5.0 6.0

0.00 1.00 2.00 3.00 4. 00 5.00 6.00 7.00 8.00

Pellet Ash Content % (Dry Basis)PM Emission Rate - g/hr

ASTM E2779

EPA Cert. Value A

A

A

A

A

B B

B

C C6 Chart 2 shows the comparison of the individual bur n rate category test runs for the two heaters whose data are shown in Table 2, us ing both low and higher ash content fuels. This limited data allows the trend of impacts on PM from ash content differences as well as showing the trend of the burn rate impact s on measured PM, at least for these two

individual heaters.

Chart 2

Pellet Heater Burn Rate Impact on PM Emissions 2 Pellet Heaters (D & E), Lower and Higher Ash Pellet Fuel

0.0 0.5 1.0 1.5

0.00 0.20 0.40 0.60 0.80 1. 00 1.20 1.40 1.60 1.80 2.00

Burn Rate - dry kg/hr5G-3(unadjusted) PM Emission Rate - g/hr

Hardwood (1.8% Ash)

Softwood (0.22-0.27% Ash) E E

E E

D
D D

D

Discussion

Although there is inadequa te data to perform a meaningful statistical test to determine if the low ash and higher ash results are from separate populations, it appears qualitatively that the trend shown in Chart 1 supports the hypothesis that higher ash pellets will produce higher levels of particulate emissions.7 The data plotted on Chart 2 help reinforce the ash effect trend shown on Chart 1 and perhaps suggests some explanation of the cause . Chart 2 shows that regardless of fuel ash content, PM emissions tend to increase when burn rate increases. The fact that pellet

heaters include combustion air blowers that creat e fairly turbulent flows within the heater burn pot and adjoining firebox area and that wh en burn rate increases, this turbulence also increases suggests that some of the additional PM collected is most probably inorganic ash that has been entrained in the exha ust flow. It is reason able to expect that when the pellet fuel ash content increases, the increase in entrained ash caused by the

turbulent flow would be exacerbated and this effect will be observed as an increase in weight of particulate matter collected. Chart 2 shows that at all but the very lowest burn rate, the higher ash pellets produce higher particulate emissi ons. Although the data are very limited, nothing known about the range of current pellet he ater designs would suggest that these trends are unique to the two tested units.

Higher ash pellet fuels dominate the available pellet fuel s upply in areas other than the west coast (primarily due to available feed stock for the pellet mills), and other potential biomass fuel options generally have higher ash contents as well. The impact of pellet ash content on emissions performance should be considered as part of the establishment of the testing requirements and passing grade for pellet heaters in the re vised NSPS. It is understood that EPA will propose require ments that address this issue

Pellet/biomass heaters can provide clean-burning heating, even on higher ash fuels. With careful consideration of the ash issue, alternative bio-fuel development and heater development for those fuels will conti nue and may provide additional attractive renewable energy options in the near future. Without that careful consideration, those activities could inadvertently be stifled.