| OCR Text |
Show Specification of the furnace fuel efficiency and exhaust port excess oxygen allows fuel and combustion air flow rates to be calculated. Heat transfer in the regenerators is calculated using a numerical algorithm in whici) the gas and brick temperatures are determined as a function of distance along the regenerator len°gth and time through the regenerator cycle3. Both convective and radiative contributions to heat transfer are considered. The radiative contribution is calculated using a radiative heat transfer coefficient 3 . The gas radiative properties are calculated using a polynomial curve fit4. The convective heat transfer coefficient is calculated by iteration to satisfy the boundary conditions. Heat loss from the furnace and air in-leakage to the regenerator are also considered by the model. Thermal analyses were performed for both baseline and reburning operating conditions. For simplicity, the regenerator convective scale factor, the fractional heat loss in the regenerator, and the total heat loss in the melter were specified to be equal to the baseline operation values. The chief variation in operation due to reburning is the introduction of reburning fuel and overfire air. These input streams are located downstream of the melter, and so represent energy which may be lost unless recovered in the regenerator. NOx Performance Estimates The potential NOx reductions achievable with gas reburning were estimated using a computational chemical kinetic, time dependent model of the reburning process. The kinetic model consists of 52 species and 200 elementary reactions. The code is assembled into a series of well stirred and plug flow reactors which represent the various zones associated with the rebuming process. The reburning fuel and overfrre air streams are injected into their respective reactors at a specified rate over a specified period of time. The mass flow rates and temperature proflles in the reburning fuel and overfrre air reactors are specified based upon the results of the process design and thermal performance analysis. Gas Reburning Performance Impacts Applying the methodology described in the previous section, conceptual gas reburning systems were developed for the model furnaces. In the approach selected, reburning fuel is introduced at the furnace port location and burnout air through multiple flush wall nozzles just above the regenerator packing. The effects of these design modifications were evaluated with the thermal analysis and kinetic models described in the preceding section. Key results are summarized in Table 1. Details of the results for the container glass model furnace are described in the following sections. Thermal Impacts The predicted impacts of reburning on overall mass flow rates and gas path temperatures for the container glass furnace are shown in Figure 6. Regenerator temperatures (brick and gas path) are slightly elevated (150°F) relative to baseline due to the introduction of burnout ~. The increased heat input to the flue gas regenerator also increases the air preheat to the primary zone by about 150°F. This increase in air preheat energy is offset by a slight decrease in mass flow due to the reduced air flow (necessary to keep primary stoichiometry, and subsequent rebuming fuel requirements, as low as possible). As a result, the primary fuel flow decreases slightly from 1992 lblhr (baseline). The rebuming fuel needed for attaining the proper reburning zone stoichiometry raises the total fuel consumption to about 7.5 percent. 6 |
