# 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 Associat ion

(HPBA)

By: Robert Ferguson Ferguson, Andors & Company

February 15, 20112 Background

Many of the EPA certified pellet heaters were teste d using pellets with very low ash content (< 0.5%). These pellets are made from soft wood feed stock and are produced in the Pacific Northwest. These pellets are commonly available for the testing laboratory that has conducted much of the pellet heater certif ication testing.

Pellets that are most commonly available in other a reas 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 would r esult in higher particulate emissions. This was based on observations made by pellet heate r manufacturers when they tested other fuel types (corn, grains, hulls, etc.) that w ere known to have higher ash content than premium wood pellets.

There was almost no data directly comparing the par ticulate emissions from low and high ash wood pellet fuels in the same heater using the same test method.

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

Data Gathering

HPBA has been working for the past six months to ob tain data that will shed some light on this issue. Some direct comparison testing 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 typic al range in terms of heating capacity.

All five heaters fell within an EPA listed heat out put range from around 7000 BTU/hour at the low burn rate settings to around 35,000 BTU/ hour at the highest setting.

We appreciate the cooperation and support of the ma nufacturers and the test laboratory that participated in this effort to gather importan t 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 report inc ludes test results from more than one test method. The testing for the results labeled “ ASTM” utilized what is now ASTM E2779, the new pellet heater operating test protoco l (that includes an integrated burn cycle covering the full range of operation of the h eater) in conjunction with ASTM E2515 for measuring particulates using a dilution t unnel. It should be noted that ASTM E2515 and ASTM E2779 report emission values “as mea sured”. The results labeled “EPA” are the EPA certification weighted average em ission rates for the heaters. If the emissions during certification testing were measure d 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 individual Method 28 burn rate category emission results but are reported as the “as measured” EPA Method 5G-3 values. The pellet moisture and ash values were de termined using ASTM E871 and ASTM D1102 respectively. Ash and moisture determin ations were conducted by qualified third party testing labs. The data are s hown 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 measur ed 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 additional pel let heaters. These heaters were tested for EPA certification using low ash pellet f uel. In addition, two individual burn rate category tests per EPA Method 28 were repeated using higher ash fuel.

Table 2

Notes: 1. Individual EPA M28 Burn Rate Category Te sts. 5G-3 emission

rate (no method adjustment). 2. EPA M28 Weighted Average (includes method 5G/5H adjustment, if applicable)5

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

Chart 1 shows the ASTM E2779 average emissions and the EPA certification emission value for each of the three pellet heaters from Tab le 1, plotted 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 burn rate c ategory test runs for the two heaters whose data are shown in Table 2, using 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 impacts on me asured 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 Pell et 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 inadequate data to perform a mean ingful statistical test to determine if the low ash and higher ash results are from separat e populations, it appears qualitatively that the trend shown in Chart 1 supports the hypoth esis 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. Ch art 2 shows that regardless of fuel ash content, PM emissions tend to increase when bur n rate increases. The fact that pellet

heaters include combustion air blowers that create fairly turbulent flows within the heater burn pot and adjoining firebox area and that when b urn 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 exhaus t flow. It is reasonable to expect that when the pellet fuel ash content increases, the inc rease 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 sh ows that at all but the very lowest burn rate, the higher ash pellets produce higher particu late emissions. Although the data are very limited, nothing known about the range of curr ent pellet heater designs would suggest that these trends are unique to the two tes ted units.

Higher ash pellet fuels dominate the available pell et fuel supply in areas other than the west coast (primarily due to available feedstock fo r the pellet mills), and other potential biomass fuel options generally have higher ash cont ents as well. The impact of pellet ash content on emissions performance should be consider ed as part of the establishment of the testing requirements and passing grade for pell et heaters in the revised NSPS. It is understood that EPA will propose requirements that address this issue

Pellet/biomass heaters can provide clean-burning he ating, even on higher ash fuels. With careful consideration of the ash issue, alternative bio-fuel development and heater development for those fuels will continue and may p rovide additional attractive renewable energy options in the near future. Witho ut that careful consideration, those activities could inadvertently be stifled.