While sugar is universally appreciated for its ability to appeal to the human palate, the production of sugar is not without its environmental challenges. The boilers used at various industrial plants including sugar mills to generate the steam and power produce NOx emissions, and reducing NOx levels is often complicated by an economic desire to fire the boilers with multiple fuels.
The Madre Tierra Sugar Mill in Guatemala was interested in adding a third fuel to its existing mix to increase its economic versatility while reducing NOx emissions. Since entering operation in 1963, the Madre Tierra mill has used a traveling grate stoker capable of firing on two fuels: stoker coal and bagasse (the dry pulpy residue remaining after juice extraction from sugar cane). In 2013, the mill decided to invest in boiler modifications that would permit firing on pulverized coal as well.
A few years ago, Forney’s ability to support such an upgrade would have been limited. With our 2014 acquisition of Pennsylvania-based Damper Design Inc., however, we added a number of complementary products to better serve our global customer base. These include a full array of damper products, low-NOx Eagle Air burners, expansion joints, air heater seals, and entry doors.
In March 2015, we commissioned our first major project involving Damper Design’s Eagle Air low-NOx burners at the Madre Tierra mill. Four 96 MMBtu/h Eagle Air burners were installed on a 70 MW Foster Wheeler power boiler supplying 450,000 lb/h of steam to the turbine-generator. The turbine-generator provides all necessary power to operate the mill, and the excess power is sold to the local grid. The project scope included our Class 1 DuraFire oil igniters and IDD flame detectors for each burner.
The Eagle Air registers automatically adjust the combustion air to the specific load. This maintains the proper fuel-to-air ratio and enables consistent low-NOx firing. The air registers can be adjusted individually according to the distribution of air delivered through the coal burners and the undergrate air from the boiler windbox. The firing rate was based on a total primary air rate of 75,000 lbs/hr, a 2:1 air/fuel ratio, and a coal heating value of 10,800 Btu/lb. Although the Raymond 713 coal pulverizer could deliver a higher fuel rate, the 2:1 air/fuel ratio provides the optimum combustion conditions.
The four DuraFire light oil, air atomizing igniters support combustion efficiency and low NOx emissions. The igniters are sized to fire 10 MMBtu/hr of No. 2 diesel at 60 psi and atomizing air at 80 psig.
Following acceptance testing of the equipment, the mill reported excellent combustion and emissions performance when firing on each of the three fuels. Bright flames and a clear boiler were reported when viewed through the tube wall ports and the furnace camera. In addition, a white plume was seen from the stack. Although NOx emissions have yet to be determined, levels are expected to be below 0.43 lb/MMBtu or 326 ppm.
In a global commodity business like sugar production, flexibility is a must. Such flexibility, however, cannot come at the expense of environmental protection. The addition of the Eagle Air low-NOx burners and the DuraFire igniters at the Madre Tierra mill in Guatemala enabled the plant to balance both objectives, efficiently firing stoker coal or pulverized coal independently or in combination with cofiring bagasse.