OCR Text |
Show probing measurements at the 6th-floor elevation to establish the baseline temperature. 02. and NOx concentration fields entering the gas injection zone, with additional temperature measurements obtained at the 6th-and 3rd-floor elevations. The resulting gas injection system provides natural gas at the 5th-floor elevation through a total of twelve wall injectors that penetrate the furnace waterwalls, six mounted in the furnace front wall, and three mounted on each sidewall. as indicated in Fig. 4. Interchangeable gas nozzles allowed injection perpendicular to the wall via 1/2-in. and 3/8-in. diameter "straight" injectors, as well as 45° downward injection via single-hole 0.45-in diameter and three-hole 0.26-in. diameter injectors. Injector hole diameters were designed to allow penetration of the gasjets across the furnace interior at 5 % nominal gas heat input without carrier gas or steam being injected with the natural gas. Performance testing of the overall fuel-lean gas reburning system at Elrama Unit 2 was conducted over a wide range of conditions. Complete test conditions and results are given in ESA Report No. 62264-1065 (see references). Major observations from these tests are summarized below. a) Gas reburning effectiveness improved when the furnace was operated at increasingly higher SOFA settings. b) Injecting more natural gas often did not yield a correspondingly higher level of NOx reduction. For example, the NOx reduction achieved at 13% gas input was essentially the same as at 5 % to 7.5% gas input. c) Introducing gas downward through the 45° injectors typically yielded a 10-15% incremental improvement in the level of NOx reduction achieved. d) The level of NOx reduction achieved was the same irrespective of whether the single-hole 0.45-in injectors or three-hole 0.26-in. injectors were used. e) The use of sidewall injectors produced less effective reburn performance than did front-wall injectors alone. Many of these performance characteristics of the gas reburn system at Elrama Unit 2 were unexpected, and represent limitations on the level of NOx reduction achievable. It was felt that LIM-based simulations of the flow, mixing, and chemistry in the facility could potentially help to identify the origins of these performance limitations, and could indicate modifications to the gas reburn system to allow higher levels of NOx reduction at lower levels of natural gas input. Accordingly, the LIM simulations described in the following section were undertaken with these objectives in mind. 3. LIM SIMULATIONS OF ELRAMA UNIT 2 LIM-based simulations were conducted of the primary coal combustion process in Elrama Unit 2 and of the overall fuel-lean gas reburn system described above. These simulations were specifically undertaken to: a) explain the overall fuel-lean gas reburning performance results that were obtained in the boiler, with particular emphasis on identifying theorigin(s) of as |