Afterburner chambers

Afterburner chambers are intended to ensure complete burnout of the off-gas. The design of an afterburner chamber shall ensure sufficient temperature, turbulence, residence time and excess of oxygen to accomplish complete off-gas burning. 

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At BASF, flammable solid, pastelike, and liquid residues are combusted in eight furnaces. Each combustion unit consists of a rotary kiln with afterburner chamber and a steam boiler. The superheated 18-bar steam from units 1 to 6 is fed into the BASF plant network. In units 7 and 8, a higher-value steam is generated with an efficiency of ca. 74 % and supplied to a back-pressure turbine, where it is expanded from 43 bar to 5 bar. To utilize the heat of the flue gases between 300 C and 180 C, a waste-heat boiler was installed to raise 5-bar steam. Electric power and 5-bar steam are fed into the respective plant systems (Fig. 113). 

Proper introduction of the off-gas into the afterburner shall ensure good mixing with the secondary air. In order to obtain sufficiently high temperatures the afterburner chamber should be provided with an auxiliary burner. 

Afterburner chambers should be of welded steel construction with an internal refractory lining, or constructed of steel that can withstand the conditions of operating temperatures and the corrosiveness of the off-gas. 

Afterburner chambers should be equipped with sight glasses, inspection hatches, connections for measurement devices and a fly ash discharge. 

The steam generator is a balanced draft, controlled circulation, multichamber unit which incorporates NO control and final burnout of the fuel-rich MHD combustion gases. The MHD generator exhaust is cooled in a primary radiant chamber from about 2310 to 1860 K in two seconds, and secondary air for afterburning and final oxidation of the gas is introduced in the secondary chamber where seed also condenses. Subsequent to afterburning and after the gas has been cooled down sufftciendy to soHdify condensed seed in the gas, the gas passes through the remaining convective sections of the heat recovery system. 

Municipal and Single-chamber incinerators Particulates, smoke, volatiles, CO, SO, Afterburner, combustion controls... 

An ethylene oxide monopropellant rocket motor is considered part of a ram rocket power plant in which the turbulent exhaust of the rocket reacts with induced air in an afterburner. The exit area of the rocket motor is 8 cm2. After testing it is found that the afterburner length must be reduced by 42.3%. What size must the exit port of the new rocket be to accomplish this reduction with the same afterburner combustion efficiency The new rocket would operate at the same chamber pressure and area ratio. How many of the new rockets would be required to maintain the same level of thrust as the original power plant ... 

TRW Systems, Inc., conducted a laboratory-scale incineration study for the U.S. Army from 1973 to 1975 (9). Eleven individual pesticide formulations and three mixed pesticide formulations containing six different active ingredients (chlordane, 2,4-D, DDT, dieldrin, lindane, and 2,4,5-T) were incinerated in a liquid injection incinerator. The experimental apparatus consisted of a fuel atomizer, combustion chamber, afterburner, quench chamber, and scrubber unit. Destruction efficiencies exceeded 99.99% for a minimum 0.4-s residence time at temperatures above 1000°C with 45 to 60% excess air. 

Figure 29.3 Experimental setup and instrumentation 1 — fuel 2 — oxidizer, N2, seed-particles 3 — plenum chamber 4 — flow straightener 5 — c/d nozzle (Dthroat = 19.0 mm, Dexu = 24.7 mm) 6 — cavity 7 — laser sheet 8 — Mie-scattering collection device 9 — CCD 10 — afterburning flame and 11 — microphone...

Fig. 12.11 shows the structure of a rocket plume generated downstream of a rocket nozzle. The plume consists of a primary flame and a secondary flame.Fil The primary flame is generated by the exhaust combustion gas from the rocket motor without any effect of the ambient atmosphere. The primary flame is composed of oblique shock waves and expansion waves as a result of interaction with the ambient pressure. The structure is dependent on the expansion ratio of the nozzle, as described in Appendix C. Therefore, no diffusional mixing with ambient air occurs in the primary flame. The secondary flame is generated by mixing of the exhaust gas from the nozzle with the ambient air. The dimensions of the secondary flame are dependent not only on the combustion gas expelled from the exhaust nozzle, but also on the expansion ratio of the nozzle. A nitropolymer propellant composed of nc(0-466), ng(0-369), dep(0104), ec(0 029), and pbst(0.032) is used as a reference propellant to determine the effect of plume suppression. The burning rate characteristics of the propellants are shown in Fig. 6-31. Since the nitropolymer propellant is fuel-rich, the exhaust gas forms a combustible gaseous mixture with the ambient air. This gaseous mixture is ignited and afterburning occurs somewhat downstream of the nozzle exit. The major combustion products in the combustion chamber are CO, Hj, CO2, N2, and HjO. The fuel components are CO and H2, the mole fractions of which at the nozzle throat are co(0.47) and iH2(0.24).

Fig. 12.17 shows a typical set of afterburning flame photographs obtained when a nitropolymer propellant without a plume suppressant is burned in a combustion chamber and the combustion products are expelled through an exhaust nozzle into the ambient air. The physical shape of the luminous flame is altered significantly by variation of the expansion ratio of the nozzle. The temperature of the combustion products at the nozzle exit decreases and the flow velocity at the nozzle exit increases with increasing e at constant chamber pressure. 

Jensen Webb (Ref 43) examined the data predicting the extent of afterburning in fuel-rich exhausts of metal-modified double-base proplnt rocket motors so as to determine the amt of an individual metal which is required to suppress this afterburning. The investigatory means they used consisted of a series of computer codes. First, an equilibrium chemistry code to calculate conditions at the nozzle throat then a nonequilibrium code to derive nozzle plane exit compn, temp and velocity and, finally, a plume prediction code which incorporates fully coupled turbulent kinetic energy boundary-layer and nonequilibrium chemical reaction mechanisms. Used for all the code calcns were the theoretical environment of a static 300 N (67-lb) thrust std research motor operating at a chamber press of S.SMNm 2 (500psi), with expansion thru a conical nozzle to atm press and a mass flow rate... 

An airtight stove with a catalytic afterburner and a smoke chamber such as a double-drum stove or a design that provides for improved burning in a secondary combustion chamber. 

Residual NHj and HCN are decomposed by afterburning under atmosphere of low oxygen concentration, but if the structure of the combustion chamber is unsuitable, a large amount of NOx will be formed here. Table V indicates that an amount of NOx is formed by afterburning in each run. Further experiments for decreasing NOx formation at afterburning of exhaust gas has been conducted... 

When pyrolytic operation is performed at air ratio for combustibles of about 0.6, it is possible not only to prevent formation of NOx, but also to reduce NOx by reducing reaction by NH or HCN in the furnace. In afterburning process of exhaust gas containing NHj and HCN, it is possible to prevent formation of NOx by two stage combustion under the condition of overall air ratio of about 1.1 and temperature at outlet of the chamber of below 950°C. 

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