Combined SO₂/NO_x removal from flue gas

Abstract

Development of a regenerative fluidized-bed process for simultaneous removal of SO, and NO, from flue gas has been underway at the Pittsburgh Energy Technology Center(PETC) since the late 1960's. In 1970, McCreaet d. [I] reported on the bench-scale evaluation of SO, removal using copper-impregnated alumina spheres and presented preliminary design criteria for a process to be used to treat flue gases from a 1000-MW utility boiler burning a 3%-sulfur coal. A copper-impregnated UOP alumina sorbent, containing 6.3 wt.% Cu, was tested over 200 cycles of SO, absorption arid regeneration with CH, in a fixed-bed bench-scale reactor. No deterioration of the physical or chemical properties of the sorbent was observed during these tests.Fluidized-bed testing(& PETC) ofthe same sorbent material was begun in 1975 using a 6-inch (15.2-cm)-diameter reactor, and the initial results were reported by Strakey et al. [Z]. The tests were conducted with the combustion products of natural gas, spiked with SO,. The SO, removal was measured as a function of solids feed rate, bed height (18 inches and 36 inches; 0.457 m and 0.914 m), and bed temperature (662°F and 750°F or 350°C and 400°C); 75 absorption-regeneration cycles were completed. During several cycles, ammonia was injected for the simultaneous removal of NO,.The results of this study were sufficiently promising to merit continued development of the process. In addition to a continuing evaluation of repeated sorptiodregeneration cycles on sorbent activity, the test program included the following: a determination of the effect of NHJNO, mole ratio on simultaneous removal of SO, and NO,; measurement of ammonia "slip" (unreacted ammonia); in situ measurements of sorbent attrition occurring in t h e fluidized bed; and an evaluation of the effect of fly ash addition on reactor performance. The results of these successful tests were reported at the 1982 Summer National Meeting of the AIChE in Cleveland , Ohio [3].Based on the results ofthe previous research, a 3 ft4 inch x 4ftOinchcross-section x 12ftOinch(1.016 m x 1.219 m cross-section x 3.658 m) high fluidized-bed absorber was designed, fabricated, and installed in a 500 lb/hr (2.268 kg/h) pulverized-coal-fired combustion test facility. A 2 ft 6 inch (0.762 m) diameter x 26 ft 0 inch (0.66 m) high regenerator was also constructed to regenerate the spent sorbent from the absorber. The results of tests conducted in this facility are discussed in this report.

Investigation of mixed metal sorbent/catalysts for the simultaneous removal of sulfur and nitrogen oxides

“…Environmental Science" cited in the program solicitation and it involves the elimination of gaseous pollutants arising from coal utilization. It is expected that this research will constitute a step in the commercial application of a new technology for the simultaneous removal of SO 2 and NO x .…”

“…The current federal NO x emission limits for combustion sources such as process heaters, industrial and utility boilers, and combustion turbines can be readily achieved by most of the NO x formation control techniques in general use. Since a significant lowering of these limits is anticipated in the near future, new methods to remove SO 2 and NO x emissions significantly and economically must be developed. It has been mentioned 1 that the pollutant emissions from coal-fired burners will be limited to one tenth of the current regulations, corresponding to about 0.06 lb pollutant per 10 6 BTU.…”

“…Several approaches may be taken to reduce the SO 2 and NO x emissions from power generation plants, such as using low sulfur fuel, removing sulfur prior to or during combustion, lowering the combustion temperature to reduce NO x formation, increasing the efficiency of the power generation systems, and removing the pollutants after combustion (stack gas cleanup).…”

Performance of silica-supported copper oxide sorbents for SOx/NOx-removal from flue gas I. Sulphur dioxide absorption and regeneration kinetics

“…Dry regenerative processes mth a copper oxide (CuO) sorbent are among the advanced processes being considewd as alternatives to the widely-used flue gas desulphumation processes based on wet once-through hlmestone scrub-bmg The CuO is deposited on a porous support to create an active sorbent with a high stabihty In the absorber of these processes, sulphur &oxide (SO,) reacts with the supported CuO and oxygen to copper sulphate (CuSO, ) at 300-450°C Regeneration is carried out with a reducing gas, e g hydrogen, carbon monoxide or methane, the copper sulphate being reduced to metalhc copper The rate of this reaction is sufficiently high at the same temperature as applied for the absorption, additional heating and/or coohng of the sorbent is therefore not required The regenerator off-gas is rmh m SO, and can be further processed to produce sulphunc acid or elemental sulphur After regeneration, the sorbent can be oxubsed and used for SO, absorption again When compared to limestone scrubbmg, CuO processes offer the advantages of (1) a small sorbent make-up, (n) producing only a relatively small amount of salable by-product, and (m) avonhng stack gas reheat and a large water consumption Furthermore, NO, can be removed simultaneously by adding ammonia to the flue gas CuO and CuSO, act as catalysts for the selective catalytic reduction of NO, [ 1,2] To date several CuO processes have been and are bemg developed The mam differences between these processes are related to the absorber design Already m the late 1960s Shell introduced the Shell Flue Gas Treating (SFGT) process with the charactenstic parallel passage reactor; a cychc operated fixed-bed contactor in which the sorbent is contamed in parallel cages [ 31. A CuO process with a fluuksed bed absorber has been developed at the Pittsburgh Energy Technology Center (PETC ) to enable contmuous operation mstead of the swmg operation of the SFGT process [ 2,4,5] However, the pressure drop for the flue gas is higher when compared to the parallel passage reactor and the allowable superficial flue gas velocity is considerably lower [6,7] We are studying the apphcation of a relatively new contactor, the gas-solid trickle flow reactor [ 81. In this reactor a ddute flow of solid particles is contacted counter-currently with the gas phase over a regularly stacked packing Favourable properties of the gas-solid trickle flow reactor are* (1) a low pressure drop, (u ) hmited axial dispersion m the gas and solids phase, (m) excellent heat and mass transfer between both phases, and (iv) counter-current operation Therefore, a gas-sohd tnckle flow reactor IS expected to be an efficlent absorber m a CuO process for the simultaneous removal of SO, and NO, from flue gases, m whmh the advantage of the contmuous operation of the flunhsed-bed process is combined with the low pressure drop and the high flue gas velocity of the SFGT process…”

“…A CuO process with a fluuksed bed absorber has been developed at the Pittsburgh Energy Technology Center (PETC ) to enable contmuous operation mstead of the swmg operation of the SFGT process [ 2,4,5] However, the pressure drop for the flue gas is higher when compared to the parallel passage reactor and the allowable superficial flue gas velocity is considerably lower [6,7] We are studying the apphcation of a relatively new contactor, the gas-solid trickle flow reactor [ 81. In this reactor a ddute flow of solid particles is contacted counter-currently with the gas phase over a regularly stacked packing Favourable properties of the gas-solid trickle flow reactor are* (1) a low pressure drop, (u ) hmited axial dispersion m the gas and solids phase, (m) excellent heat and mass transfer between both phases, and (iv) counter-current operation Therefore, a gas-sohd tnckle flow reactor IS expected to be an efficlent absorber m a CuO process for the simultaneous removal of SO, and NO, from flue gases, m whmh the advantage of the contmuous operation of the flunhsed-bed process is combined with the low pressure drop and the high flue gas velocity of the SFGT process…”