New Catalytic Combustion Technology for Very Low Emissions Gas Turbines

Abstract

A catalytic combustion system has been developed which feeds full fuel and air to the catalyst but avoids exposure of the catalyst to the high temperatures responsible for deactivation and thermal shock fracture of the supporting substrate. The combustion process is initiated by the catalyst and is completed by homogeneous combustion in the post catalyst region where the highest temperatures are obtained. This has been demonstrated in subscale test rigs at pressures up to 14 atmospheres and temperatures above 1300°C (2370°F). At pressures and gas linear velocities typical of gas turbine combustors, the measured emissions from the catalytic combustion system are NOx < 1 ppm, CO < 2 ppm and UHC < 2 ppm, demonstrating the capability to achieve ultra low NOx and at the same time low CO and UHC.

Task 8.2 - subscale catalytic combustor development

“…If the gas temperature is sufficiently high, homogeneous cornbustion within the catalyst is initiated, leading to gas temperatures close to adiabatic combustion temperatures corresponding to the global equivalence ratio. A schematic of the design of a conventional catalytic combustor allowing homogeneous combustion within the catalyst bed is shown in Figure 1 (from Dalla Betta et al ., 1993). At these high bed temperatures, problems of thermal sintering of support surface area, sintering and vaporization of active catalyst components (e.g.…”

“…At these high bed temperatures, problems of thermal sintering of support surface area, sintering and vaporization of active catalyst components (e.g. Pd) and thermal shock fracturing of ceramic substrates could occur (Dalla Betta et at., 1993). This is one of the major limitations of a conventional catalytic combustion system.…”

“…The obvious advantage of this strategy is the substantially lower substrate temperature, which allows higher catalyst activity in the initial stage (where the gas temperatures are low), and a lower catalyst activity in the later stages since a higher gas temperature is provided by reactions in the inlet stage. A schematic of the Catalytica catalytic combustion design is shown in Figure 2 (from Dalla Betta et al, 1993 Catalyst bed design is based on an available catalyst operating window, a typical example of which is shown in Fgure 3 for the ATS-S engine cycle. The catalyst ignition temperature is approximately 7OO0F, and is relatively independent of the fuel-air ratio.…”

Field Test of a 1.5 MW Industrial Gas Turbine With a Low Emissions Catalytic Combustion System

“…For the catalytic combustor system described in this report, the catalyst system is designed to combust only a portion of the fuel in the catalyst with the remaining fuel combusted homogeneously just downstream of the catalyst (Dalla Betta, 1994). All of the fuel is mixed with air at the catalyst inlet.…”

“…Typically, 50% of the fuel is reacted in the catalyst and the remaining fuel is combusted in a post catalyst zone to achieve temperatures in the range of 1200° to 1500°C (2190° to 2730°F). Rig tests at high pressure and at gas velocities typical of those encountered in a gas turbine combustor have demonstrated NOx emissions of -A ppmv at 15% 02 for combustor outlet temperatures of 1300°C (2370°F) and -2.3 ppmv at 15% 02 for combustor outlet temperatures of 1500°C (2730°F) (Dalla Betta, 1994). To demonstrate this technology in an operating gas turbine, a catalytic combustor system was developed for the Kawasaki MIA-13A gas turbine.…”