The Alberta Research Council evaluated the performance of the All Canadian Boiler & Hydronic Heating System manufactured by Nova Metal Tech Ltd. (NMT). These units are stoker coal-fired combustion systems that produce hot water for building heating and other purposes. The unit tested was rated at 2.3 million Btu/hr.

Two tests were performed at the NMT manufacturing site; one with the unit operating at 65% coal feed rate and one with the unit operating at 100% coal feed rate. The unit was installed and operated by NMT personnel. After reaching steady state conditions, each test lasted about 1 hour with the following measurements taken:

• Total coal feed over a measured time to determine coal feed rate and thermal input
• Feed water flow rate and temperature rise to determine useful heat output
• Temperature and composition of flue gas to determine combustion efficiency, flue gas thermal losses and emissions of SO₂, NO₂ and particulates
• Coal and ash sample analysis for energy calculations and combustion efficiency

The unit tested was recently built and in clean condition and would be expected to operate near maximum efficiency. At 65% coal feed rate the measured useful heat output, as hot water, was 508 kW (1.73 MMBtu/hr) with a thermal efficiency of 84.3%. On average, the flue gas for Test 1 was at 165ºC and contained 6.7 vol% O₂, 12.8 vol% CO₂, 54 ppm CO and 209 ppm NO_x.

For the second test at 100% coal feed rate the measured useful heat output was 906 kW (3.09 MMBtu/hr), with a thermal efficiency of 82.9%. On average, the flue gas for Test 2 was at 195ºC and contained 5.5 vol% O₂, 13.4 vol% CO₂, 198 ppm SO₂, 73 ppm CO and 216 ppm NO_x.

The above thermal efficiencies were calculated from flue gas temperature and composition and the feed coal properties. Calculating efficiency based on coal energy input and hot water energy output was not possible in Test 2 due to variability of density and heating value of the coal and changes in cooling water flow rate during the run. Due to the short run time of the experiments, an accurate ash balance and representative unburned carbon in ash number could not be determined.

Based on the measured test data, operation of the unit with 5 to 7% oxygen concentration in the flue gas provides sufficient excess air to keep carbon monoxide levels below 100 ppm. For combustion of coal, flue gas temperatures should be maintained above 136ºC to minimize stack corrosion.