This report summarizes available information on the operational changes and environmental impacts of burning of tire-derived fuel (TDF) in boilers, and petcoke in lime kilns and recovery furnaces. It serves as an update to similar information contained in NCASI Technical Bulletin No. 906.

Air emission impacts from burning TDF are generally small to non-existent with the possible exception of elevated levels of zinc in combustion ashes and occasionally also in stack emissions. NOx, CO, and total hydrocarbon (THC) emissions generally remain unchanged. SO2 emissions also remain unchanged, but may increase slightly if the majority fuel being replaced is bark or gas. Particulate matter (PM) emissions will remain unchanged unless the TDF replaces oil or gas and an adequate PM control device is not present. TDF burning has no impact on dioxin/furan emissions from a boiler.

Limited data on the impact of petcoke burning in lime kilns on emissions of PM, CO, total reduced sulfur and total volatile organic compounds (or THCs) suggest these impacts to be negligible or small. The overall impact of petcoke S content on SO2 emissions from the lime kiln appears to be no different than the impact of other forms of S inputs to the kiln, including sulfur contained in low volume high concentration non-condensible gases, stripper off-gases, fuel oil, and rectified methanol. Pre-wet scrubber or post-electrostatic precipitator kiln SO2 emissions appear to be negligible up to a certain amount of S input to a kiln (close to 10 lb S/ton CaO). Beyond this amount, a linear relationship between kiln S input and kiln S output (as SO2) is observed with roughly two-thirds of the sulfur input being captured within the kiln. It appears that both Na and Ca present in the mud play a role in the S capture mechanisms within a kiln under different circumstances, with the fuel S leaving the kiln both as CaSO4 and Na2SO4 within the lime product. Firing petcoke in lime kilns can increase the sulfidity and vanadium concentrations in the mill’s black and white liquors.

With a wide range of NOx emissions observed from the same kiln with similar amounts of petcoke substitution, the data suggest a complex relationship between petcoke burning and lime kiln NOx emissions. Occasionally, a particular kiln exhibited a linear relationship between short duration NOx emissions and the level of oxygen in the kiln’s stack. However, most of the data did not adhere to such a relationship. Petcoke N content did not appear to be an important factor in determining kiln NOx emissions, since the measured NOx emissions amounted (at worst) to very small fractions of N-to-NOx conversion rates (<5%). It is suspected that just as in the case of natural gas firing in lime kilns, petcoke firing results in differing hot end temperatures depending on the way the kiln is operated, perhaps introducing an element of thermal NOx contribution to the overall NOx emissions.

Insufficient data are available to understand whether petcoke can be fired in a kraft recovery furnace without any harmful effects. No data are available on petcoke burning in bark boilers. Much of the boiler data correspond to boilers where coal is replaced by petcoke and some form of flue gas desulfurization is already available.