Research Boiler System
Penn State’s research boiler is a 1,000 lb saturated steam (@ 150 psig)/h watertube boiler of A-Frame construction that was designed and built by Cleaver Brooks. The combustion chamber is 3x3x7 ft (63ft3) with a maximum heat release rate of 42,000 Btu/ft3-h. It contains 288 ft2 of heating surface and the maximum firing rate is two million (MM) Btu/h (60 Hp).
The boiler is equipped with eighteen side ports for gaseous and particulate sampling. Fourteen of the ports have diameters of 3 inches and four have diameters of 4 inches. The combustion gases split into two convective sections, one on each side of the radiant combustion chamber. There are access doors into each of the convective sections. There are also two ash hoppers under each convective section and there is a doorway into the radiant combustion chamber.
The steam pressure is maintained constant at 150 psig during testing by a back-pressure regulator. The steam flow rate is measured by a steam flow meter before passing through a condenser. The condensed steam flows into a feedwater tank before returning to the boiler.
The boiler, designed for natural gas and oil, has been retrofitted to fire coal-based fuels. To promote and enhance combustion, a ceramic burner throat extends the combustion chamber by two feet. This ceramic section, termed a quarl, is preheated by a natural gas flame prior to introducing the coal. The quarl aids in the support of hard to ignite fuels by storing some of the radiant heat energy released by the flame.
A gas-fired combustion air preheater supplies over 300,000 Btu/h to preheat up to 1,200 lb/h of air to 350°F. The preheated combustion air (secondary air) is passed through a conventional swirl ring several inches before the gas distribution ring, both of which were 8 inches in diameter. A small portion of unheated primary air is fed through an annulus gap surrounding the nozzle. Preheated primary air is introduced into the quarl tangentially through two headers that are balanced for uniform flow.
Flue gases are cooled below 500°F in an economizer prior to passing through a bag filter. The bag filter contains sixteen 5 inches diameter by 96 inches high-temperature bags sewn with felted P84 fibers.
Barrel heaters will be used to preheat the liquid fuels prior to atomization/ combustion. The fuels will be heated to typical heavy fuel oil temperatures (>200°F) for the testing.
During testing, once the desired firing rate is obtained, data are recorded by the operators and ash samples are taken every half-hour from the baghouse and hoppers (when firing ash-containing fuels). Data are also logged by the data acquisition system at one-minute intervals, which include, temperatures, pressures, flow rates and flue gas composition (O2, CO2, CO, NOx, and SO2). When ash samples are collected, they are analyzed for moisture and ash to calculate the combustion efficiency.