GB2401373A - Reduction of NH3 and NOx from gasified fuels - Google Patents

Abstract

A process for the reduction of ammonia and nitrogen oxide emissions from e.g. a power plant, comprises reacting ammonia with a stoichiometrically deficient quantity of oxygen , to form NO and water. The NO is then catalytically reacted with carbon monoxide to from nitrogen and carbon dioxide.

Description

Introduction

A hot gas clean up method that would circumvent the formation of NOx in integrated gasification power plant is to use a selective catalytic oxidation technology as a fuel processing scheme. Recent and on going development work on gasifier stream have used Al2O3 catalyst, NiO catalyst with reactive oxidisers such as air and NO to promote the SCO reaction in the hot fuel gas stream(1,2). Other catalysts have been studied under the same theme but on laboratory scale and have been reported in the literature(3-6). The literature cites work in this field where tests have been conducted on catalysts using fuel gas whose composition deviates from the actual composition that one would normally encounter in a gasification process, particularly the CO and H2 content (7,8), the latter contribute to the overall reaction of the process.

This invention will promote the use of renewable fuel such as biomass, municipal waste, coal, plastic, tyres, heavy residue oils in gasification power plant and will consequently help towards their environmental and economic acceptability. This invention is one that is capable of operating at both high pressure(at gas turbine operating pressure and fuel mass flow) and atmospheric. It is a fuel processing unit design to rid the fuel of the NH3 in the hot gas stream. The features of the invention are based on the results of tests carried out and reported in the result and experimental sections.

The features of the process are depicted in the examples 1, 2 and 3. It makes use of the differences that exist in reactivity between the individual constituents of the fuel.

For instance, NH3 will persist in presence of large concentration of H2, but it can be made to react preferentially with O2 to form NO, NO2 below a certain critical amount of H2. This scenario is allowed to develop in a controlled fashion by first catalytically promoting H2 combustion and subsequently the NH3 will react competitively for the O2 to form NO. The site specific catalytic reaction of NO with CO in the right temperature range over the second stage catalyst is favourable provided the amount of H2 is below the critical value, otherwise the conversion efficiency is compromised.

The variable components of the invention are: À the amount of O2 added as process air À the catalysts formulations for the 2 catalytic stages À the H2 combustion reaction for stage 1 À the NO + CO reaction for stage 2 \, À the catalysts sizing to achieve the desired reactions À the mixing and temperature profile of the reacting fuel gas The invention is a fuel processor that arises when the above 6 items are packaged together. Every fuel processor is sized to treat the fuel gas at conditions of mass flow, temperature and pressure to meet the fuel requirement of the engine, as shown in examples 2 and 3. This invention is making use of selective catalytic oxidation of the NH3 in the hot fuel gas stream by addition of controlled amount of air as oxidiser and in turn the NH3 is converted to N2 through a series of both catalytic and gas phase reactions.

The performance results are summerised in Table 1 and forms the basis of the invention.

Table 1

Partial Pressures kPa:1 GHSV h-, Blend N2 H2 CH4 NH3 H2O CO2 CO 02 cony. X10 x10a LV T u/s T d/s No. % Cat Cat 2 m/s C C 32b 229.6 42.7 0 0.18 0 0 0 7.5 nil 3.1 6.8 415 751 28b 221 9 44 5 O J:4 24 7 O 7 7 as 3 3 1 6 9 10 416 758 27b 243.1 42.1 5.2 0.18 0 0 0 7.9 nil 3.3 7.3 10 427 709 23b 247 0 42 4 5.2 0 4 0 0 0 6 9 18 3 3 3 7 2 10 429 699 21 b 234.1 41.0 5.0 0.38 0 0 36.5 9.7 74.4 3.8 8.3 11.6 427 726 20b 248.4 41.9 5.2 0.4 0 0 0 9.9 13.3 3.5 10.7 10.7 422 738 18b 188.9 41.6 5.1 0.39 0 0 55.4 9.8 52.5 3.3 7.6 10.6 424 745 17b 164.6 43.2 5.3 0.4 0 23.9 57.2 7.0 73.0 3.3 7.2 10 437 683 13b 156.0 43.6 5.3 0.4 12.8 24.2 58.1 7.1 88.8 3.3 7.3 10 448 689 12b 164.3 43.4 5.3 0.59 0 24.1 57.8 7.9 93.1 3.3 7.2 10 435 688 11b 165.0 43.2 5.3 0.8 0 24.0 57.5 7.8 94.8 3.3 7.2 10 431 686 8b 167.0 327 53 08 0 109 580 78 907 31 89 9.5 431 888 The utilization of biomass as an energy source for thermal power generation in an IGCC has drawn special interest in the past decade and the trend is set to continue.

The attraction is that biomass derived fuel can be generally considered as being CO2 neutral and hence does not make any net large contribution to global warming.

However, there still remains a pertinent point that requires further development work, which is the NH3 contained in the fuel. If not removed, it would be oxidised to NOx(fuel bound NOX) in the gas turbine combustor and the level emitted would far exceed any guide values. The amount of NH3 in the fuel can be large, up to 4000ppm(9-12). The heat value of gasified biomass fuel is typically one tenth to half that of natural gas. The practical solution to date is to waterwash the fuel resulting in lower NH3 (50ppm) content, a loss to the thermodynamic cycle, and the need to dispose of the waste stream.

There are 2 possible NH3 destruction reactions which are (i)complete pyrolysis/thermal decomposition (ii) oxidation of the NH3 2NH3 N2 + 3H2 2NH3 + 3/2O2 N2 + 3H2O Thermal decomposition occurs at 900 C, whilst oxidation in air starts at around 600 C. Under excess oxygen, the following reaction occurs 2NH3 + 5/2O2 2NO + 3H2O The latter reaction is influenced by the presence of the other combustibles in the fuel mix, namely H2 and CO. The aim of the present study is to promote the formation of NO in the fuel mixture followed by the subsequent catalytic reaction of the NO with CO to form N2 and CO2.

The experiments that led to the invention were conducted at pressure up to 5 bar, using catalytic combustion with reaction-specific catalysts to reduce the NH3 level in the fuel gas without the disadvantage of the thermodynamic loss to the engine cycle, and the waste disposal. The results focus on the catalytic conversion of NH3 to N2 at a gas solid interface using a monolith catalyst under controlled oxygen atmosphere.

The catalysts investigated are supported Rh/AI2O3, PVRh/AI2O3, and Pt/Pd/SnO2, using a synthetic biomass fuel gas blended from individual gas streams to make up the desired composition. Details of the catalytic reactor and the combustion rig set up are presented. The reaction is sensitive to temperature and NH3 conversions of up to 90% have been achieved. The temperature of the catalyst bed is maintained by fine controlled of small amount of oxygen fed as air.

Experimental Testing in a small scale high pressure test rig under conditions approaching those of a gas turbine was undertaken. The test rig is shown in Figure 1. The synthetic fuel gas which resembles the biomass fuel is blended from individual components. The catalytic combustor/reactor is shown in Figure 2. It is made up of catalysts entities of different formulations that has been prepared and arranged in the holder so as to take advantage of the differential between the reaction rates and characteristics of the various constituents of the fuel. The catalytic combustor/reactor has two main aims, carried out in a two stage catalyst arrangement with 3 formulations tailored for specific tasks. These aims are to burn H2 preferentially in the first stage and raise the temperature substantially for the second stage, where the NO and CO catalytic reaction can occur favourably on the front end of second stage. The back end of the second stage promotes the pyrolysis of the NH3. The catalytic reactor is behaving as a fuel processing unit capable of operating over an inlet temperature range of 415 - 45o C.

The catalyst substrate for both stages is cordierite honeycomb with square cells. The first stage is 30 mm in diameter and 11 mm long. The dimensions of the second stage are 30 mm in diameter and 50 mm long. Both with 400 cells per square inch.

The first stage has a 20% SnO2 washcoat loading which has been sintered to give a stabilised surface area of less than 50 m2/g. The precious metals are deposited sequentially from chloride free precursors, with palladium first followed by platinum.

This catalyst is calcined in air, reduced in H2, and stabilised in air. The metal loadings are Pt 0.9% and and Pd 1.0%. The second stage monolith carries a washcoat of 22% La/AI2O3. The monolith is impregnated with rhodium nitrate solution and calcined in air at 500 C resulting in a 2% loading of rhodium on the surface as the active phase. In addition, the rear end of the second stage carries 0.9% Pt.

The fuel composition was typical of biomass gasification and contained approximately 20% CO. The tests were carried out at 400 kPa, using synthetic gasified biomass as the fuel and blended from individual components. The fuel contained the specified target concentration of each component as depicted in Table 2. In some experiments the water was omitted.

Table 2 - Fuel composition Components % volume % mass Nitrogen 46.40 53. 59 Carbon dioxide 8.10 14.70 water 9.10 6.75 Carbon monoxide 19.50 22.52 Hydrogen 15.10 1.25 Methane 1.80 1.19 Total 100.0 100.0 Average net CV (MJ/kg) 4.364 Average molecular mass (kg/kmol) 24.244 Ammonia ppmv 1500 The catalytic combustion on the first catalyst stage was finely controlled by the amount of air admitted and served two purposes, firstly to raise the temperature, and secondly to promote the oxidation of the NH3 to NO in the gas phase in an oxygen deficient atmosphere. The exotherm was predictable in magnitude and was mostly due to the combustion of some H2 and some CH4. The subsequent catalytic reaction of NO with CO to N2 on the second catalyst stage, with some NH3 decomposition following on. The former reaction on the catalyst surface is site specific.

The remaining unburnt combustibles were ignited downstream in a burnout tube after addition of excess air from a compressor, the exhaust temperature rose to 750 C, and was controlled with only one water cooling spray injector in operation. The exhaust gas was vented through a muffler and an extractor fan to the outside.

The fuel preparation prior to delivery to the catalyst are shown in Figure 1. The ballast N2 was metered by a Coriolis meter. By virtue of the chemical reactivity of the ammonia, it was fed cold, as was the process air in order to avoid autoignition in the heater. Additional trace heating to the pipework leading to the catalyst was required in order to avoid excessive heat loss. The catalyst operating temperature range was 680 750 C. The CO, H2, CH4, CO2, H2O together with the ballast N2 made up the bulk of the fuel and was heated by a single pass through a 36 kW electric heater. The - Hi' small amount of oxygen required for the NH3 to NO reaction came from the air injection. The oxygen content of the latter served a further purpose which was to raise the catalyst bed temperature to the desired set point temperature, by combusting some H2 and CH4 on the catalyst surface. Gas analysis of all components was carried out using a series of dedicated instrumentations, NOx by chemiluminescense, CO by non dispersive infra red, CO2 by infra red, NH3 was measured independently by 2 methods - FTIR and infra red, and CH4 by FID.

A spatially uniform mixture of all the fuel components with the process air in front of the catalyst is a prerequisite. Mixing was achieved by using 2 elements of a proprietary mixer (SULZER type SMV) in line, in front of the catalyst. Figures 2 and 3 show the mixer assembly together with the thermocouple positions, pressure transducer locations and the sample gas offtake positions. in.

The catalyst selection and its performance were based on the results of 2 reactions: (1) addition of limited amount of oxygen (defined as process air) so as to promote the gas phase oxidation of NH3 to NO Gas phase 2NH3 + 5/2O2 2NO + 3H2O (2) The surface reaction of NO with CO at the Rh/AI2O3 interface whereby the NO is reduced to N2 Catalytic Rh/AI203 2NO + 2CO N2 + 2CO2 This invention takes advantage of the inter- relationships that exist between the constituents of the fuel gas and in particular CO2, CO and H2 vis a vis NH3 reactivity over the catalyst at conditions of temperature, pressure and to deliver a satisfactory catalysts performance as far as NOX formation is concerned. The results are summerised in Table 1 and shows the extent of NH3 conversion on the catalysts for varying blends and eventually approaching a characteristic low calorific value nitrogen bearing fuel.

The invention Gasified biomass is a low calorific value fuel containing 7 components in equilibrium at a specified pressure and temperature usually 400 C and 10 bar.

The typical composition is Components of Fuel Volume % (normal) N2 51.93 H2 14.51 CH4 1.77 NH3 0.14 H2O 4.25 CO2 8.06 CO 19.35 During combustion, the ammonia is oxidised to NOx which exceed any acceptable level. When such a fuel gas is synthesised by blending the mixture from individual components for the purpose of determining combustor performance, the resultant mixture is a non equilibrated one. This is due to gas phase and some heterogeneous catalytic reaction between CO, CO2, H2 and the NH3 at the operating temperature and pressure. Initial experiments conducted when synthesising this fuel have shown a substantial reaction between the CO and NH3. If the presence of NH3 is followed, then the results show a depletion of NH3 when CO is introduced.

Table 3 - Fuel blend 32b Temp.u/s 41! i C, Temp. d/s 751 C, LV 9 m/s, Pres sure 328 kPa Measured at Measured at Components Calculated upstream of downstream of vol.% catalyst catalyst N2 83.7 H2 13.8 11.7% 7.65% CH4 O O.12% 400ppm NH3 0.06 664ppm H2O O O O CO2 O 500ppm 700ppm CO O O 100ppm O2 2.4 2.64 1300ppm NO O 3ppm Oppm CO, CO2, and H2O are absent in fuel blend 32b, the amount of NH3 added agrees with the amount measured at the upstream position. A small amount of methane is being measured (0.12%) possibly due to some insignificant methanation reaction taking place in the heater, starting from existing carbon deposit. The amount of H2 measured at the upstream is 2% less than the calculated amount added, which suggests that some reaction is taking place in the heater. CO measurement downstream of the catalyst indicates that partial combustion of the insignificant amount of methane has occured on the catalyst. The point to note is that the NH3 added corresponds to the amount measured at the downstream position when CH4, CO and CO2 are absent in the blend at the steady operating conditions of pressure, temperature and linear velocity as shown in Table 3.

Table 4 - Fuel blend 28b Temp.u/s 418 C, TemP. d/s 758 C LV 10 m/s Pressure 328 kPa Measured at Measured at Components Calculated vol. % upstream of downstream of catalyst catalyst N2 76.5 H2 13.6 8.41 % 3.7% CH4 O 0.02% Oppm NH3 0.06 208ppm H2O o 0 0 CO2 7.5 5.28% 5.5% CO O 2. 84% 3.1% O2 2.4 2.8% 1500ppm NO O 3ppm 1 ppm Fuel blend 28b has CO2 added to blend 32b as shown in Table 4, substantial reaction takes place in the heater. Some of the CO2 has reacted with the H2 to form C0(2.84%) and a very small amount of CH4(0.02%) leaving behind 5.2% CO2. A 5.2% consumption of the H2 in the heater, leaving 8.41% (the measured value) at the catalyst upstream position is observed. A corresponding amount of air is added cold to give an equivalent 2.4% O2 which mixes with the hot blended fuel gas. The O2 measured at this point indicates a 0.4% increase by volume. This observation is not common and can possibly be due to some pertubations in the processed air mass flows.

The catalyst downstream measurement shows that 4.7% of the H2 has been partly used up on the catalyst and or partly burned. The insignificant amount of CH4 has been oxidised leaving no trace, there is a marginal increase in CO and CO2. The O2 left is 0.15% with 94% consumed in the catalyst. The NOX measured is 1ppm, this is not surprising as the bed temperature is low and remained constant at 770 C. The important feature of this dataset when compared with Table 3 is the fate of the NH3, which shows a 65% disappearance when CO2 is added. This result suggests that the CO generated in the heater from the CO2, reacts with the NH3 to yield a substantial amount of an amide compound. The latter being formed between CO2 and NH3 and is not being identified and followed through here. The reaction between CO2 and NH3 under the given sets of conditions here is also playing a contributive role, thus yielding the amide compound which resembles urea (NH2-CO-NH2). The latter is sometimes used instead of NH3 in SCR DeNOx plant to reduce NOX. This reductive method assumes the formation of NO first, thence 2NH2-CO-NH2 + 4NO + O2 4N2 + 4H2O + 2CO2 In the presence of a strong oxidation catalyst such as a Pt based one, any NO formed will be oxidised to NO2, and the subsequent mixture of NO-NO2 will react faster according to the SCR reaction.

4NH3 + 2NO + 2NO2 4N2 + 6H2O The SCR reaction is the basic one 4NH3 + 4NO + O2 4N2 + 6H2O ' Table 5 - Fuel blend 27b Temp.u/s 4. 27 C, Temp. d/s 709 C, LV 10 m/s, Press' are 328 kPa Measured at Measured at Components Calculated vol.% upstream of downstream of N2 83. 2 catalyst catalyst H2 12.8 11.3% 9.5% CH4 1.6 1.51 % 0.66% NH3 0. 06 637DDm H2O o 0 0 CO2 0 500ppm 0.28% CO 0 0 0.73% O2 2.4 2.1 % 1700ppm NO 0 2ppm 0 The mixture given in Table 5 refers to fuel blend 27b and is similar to fuel blend 32b except that CH4 is intentionally added whilst CO, CO2 and H2O are omitted. The catalyst upstream measurement shows a 1. 5% decrease in H2 and a 0.09% decrease in CH4 with a corresponding formation of 500 ppm CO2, all occuring in the heater. Moreover there is no CO being detected and the O2 is slightly lower by 0.3%.

The catalyst downstream measurement shows that 1.8% of H2 is burned on the catalyst. The catalyst has oxidised some of the CH4 to give 0.28% CO2 and 0.73% CO, leaving 0.66% CH4 as unreacted hydrocarbon. The resultant O2 is 0.17%.

corresponding to consumption of 95% of the O2 admitted. There is no significant change to the NH3 (637ppm) at the downstream position. This suggest that the addition of CH4 does not directly interfere in the reaction involving NH3, presumably because there is no CO present at the catalyst upstream position, as seen in Table 4.

Table 6 - Fuel blend 23b Temp.u/s 4: '9 C Temp. d/s 699 C, LV 10 m/s, Press ure 328 kPa Measured at Measured at Components Calculated vol. % upstream of downstream of catalyst catalyst N2 83.2 H2 12.9 11.4% 9 0% CH4 1.59 1.6% 0.67% NH3 0.12 980DDm H2O O O O CO2 0 400ppm 0.24% CO 0 0 0. 71 % O2 2.1 3.18% 1800ppm NO 0 2ppm 1 ppm ' The fuel blend in Table 6 corresponds to blend 23b and is almost identical to that of 27b, except that twice the amount of NH3 is added. The point to note here is that as CO is not formed in the heater, that is at the catalyst entry there is no CO present (whilst H2 is in substantial amount). The resulting effect on the NH3 downstream of the catalyst has been a relative small drop in level and this shows a clear relationship between the two. About 58% of the 1.6% CH4 is oxidised on the catalyst to give 0.24% CO2 and 0.71% CO. The O2 remaining is 0.18%. This dataset confirms the one in Table 5, that is the CH4 does not interfere with the NH3 concentration in a blended mixture so long as the latter does not contain CO, even though the NH3 level is higher.

Table 7 - Fuel blend 21 b Temp.u/s 42 7 C, Temp. d/s 726 C, LV 11.6 m/s, Pres. lure 363 kPa Measured at Measured at Components Calculated vol. % upstream of downstream of catalyst catalyst N2 74.5 H2 11.3 9.1% CH4 1. 38 1.6% . NH3 0.11 282ppm H2O O O CO2 0 1.16% 2.1% CO 10.0 7.51 % 7.6% O2 2.7 2.88% NO 0 1 ppm 1 ppm As shown in Table 7, when 10% CO is added to a similar mixture as in Table 6 to give Fuel blend 21b, (ie without CO2 and H2O), the effect of the level of NH3 is demonstrably clear, with 75% of the NH3 disappeared. At the upstream position there is 9.1 % H2 suggesting that 2.2% has been used up in the heater for a reforming reaction. A slight increase in the CH4 is also noted at the upstream position. The catalyst upstream measurement indicates that some CO2 has been formed and there still remains substantial amount of C0(7.5%). This result further confirms the observation that the disappearance of NH3(75%) is associated with the presence of CO in the gas mixture. This is a truely catalytic effect, the catalytic reaction is proceeding at 747 C and 363 kPa with 9.1% H2, 7.51% CO, 2.88% O2 over the 2 stages of catalysts. Additionally, the NH3 is reacting concomitantly with the CO to form an amide compound -CONH2, and which is acting as a reductant as in a SCR DeNOx process.

Table 8 shows the data for Fuel blend 20b where the CO is removed from blend 21b and the difference is made up with N2 and the result conclusively confirms the reactions between NH3 and CO and O2 are occurring under the present operating conditions. The explanation for the reduction in the NH3 that is manifested when CO is added can be explained by the fact that the surface catalytic reaction on the stage 2 catalyst is a fast one and first assumes the formation of NO. The latter reacts with CO at the Rh/AI2O3 interface and the NO is reduced to N2 Gas phase 2NH3 + 5/2O2 2NO + 3H2O Catalytic Rh/AIz03 2NO + 2CO N2 + 2CO2 Both reactions proceed satisfactorily at low H2 partial pressure, otherwise both are suppressed. The first stage catalyst ensures that the reactants composition at the inlet of the stage 2 catalyst are within the optimum range to ensure the NO + CO catalytic reaction shown above. The duty of first stage catalyst is to oxidise as much of the H2 at the given linear velocity and to competitively allow for the formation of NO.

Table 8 - Fuel blend 20b Temp.u/s 42. 2 C, Temp. d/s 738 C, LV 10.7 m/s, Pres sure 343 kPa Measured at Measured at Components Calculated vol. % upstream of downstream of N2 83.28 catalyst catalyst H2 12.2 10.78% CH4 1.5 1.51 % 0.65% NH3 0.11 953ppm H2O O O CO2 0 700ppm 0.25% CO 0 0. 77% O2 2.88 2.99% NO 0 2ppm 0 - t1 Table 9 - Fuel blend 18b Temp.u/s 424 C Temp. d/s 745 C, LV 10.6 m/s, Pressure 338 kPa Measured at Measured at Components Calculated vol.% upstream of downstream of N2 66. 8 catalyst catalyst H2 12.3 8.86% 8.6% CH4 1.5 0.83% NH3 O.11 523ppm H2O O 1.53% 2.6% CO 16.4 13.4% O2 2.90 NO O 4ppm 7ppm When CO is reintroduced to the mixture to give fuel blend 18b (Table 9), the level of NH3 downstream of the catalyst shows a reduction of almost 50% to 523ppm. It is worth noting that although CO2 was not added to the blend, it was measured (1.5%) upstream of the catalyst. Its origin could be in part from the CH4 and the coke in the heater. The overall H2 consumption from rig inlet to the downstream of the catalyst amounts to 3.7% and approximately half of the CH4 have been burned on the catalyst. In effect the addition of CO further confirms a possible reaction taking place between CO and NH3 via NO.

Table 10 - Fuel blend 17b Temp.u/s 437 C Temp. d/s 683 C LV 10 m/s Pressure 328 kPa Measured at Measured at Components Calculated vol. % upstream of downstream of catalyst catalyst N2 58.2 H2 13.2 9.40% 8.8% CH4 1.6 1.8% 1.22% NH3 O.12 323ppm H2O o o CO2 7.3 7.0% 8.15% CO 17.4 18. 1% O2 2.1 2.2% 0.69% NO O 3ppm Oppm Addition of CO and CO2 to the mixture, gives a fuel blend 17b (Table 10) which resembles that of coal gasification (without water) in composition. Some reforming/methanation reaction takes place in the heater resulting in a 3.8% decrease on H2 and a further 0.6% H2 is burned on the catalyst. Some of the CH4 is burned on the catalyst to form CO2 and CO downstream of the catalyst which is À 1measured as an overall increase of 0.85% for CO2 and 0.7% for CO. The data shows that for this typical fuel blend, the amount of NH3 remaining after this catalyst arrangement is 27% and leaving a fuel containing substantial amount of H2 and CO and CH4 at 695 C.

Table 11 - Fuel blend 13b Temp.u/s 448 C, Temp. d/s 689 C, LV 10 m/s, Pressure 338 kPa Measured at Components Calculated vol.% downstream of catalyst N2 55.0 H2 12.9 10.3% CH4 1.6 0.69% NH3 O.12 135ppm H2O 3.8 CO2 7.2 9.1% CO 17.2 17.0% O2 2.3 0.7% NO O 1 ppm: Table 11 refers to fuel blend 13b and shows the results when 3.8% H2O is added to blend 17b mentioned in Table 8. This synthetic gas mixture has all the components of a low cv fuel from a gasification process. The NH3 remaining is down to 135ppm from 1200 ppm, a reduction of 89%. The result is consistent with the observations of the previous mixture. It is worth noting that less than 4% H2 is consumed between the rig inlet and the catalyst exit and some of the CH4 is converted to CO and CO2.

Table 12 - Fuel blend 12b Temp.u/s 435 C Temp. d/s 688 C LV 10 m/s Pressure 333 kPa Measured at Components Calculated vol.% downstream of cablyst N2 58.2 H2 13.0 10.4% CH4 1.6 1.1% NH3 O.18 123ppm H2O O CO2 7. 3 8.7% CO 17.4 17.1% O2 2.4 0.77% NO O Oppm The main features of the three fuel blends shown in Table 12, Table 13 and Table 14 are that there is no addition of water, and the level of NH3 are 0.18%, 0.24% and 0.26% respectively whilst keeping the concentration of the other components as near constant as possible, except in the last case (Table 14) where the level of CO2 in the blend is halved. In all three cases substantial amount of NH3 has disappeared (90%).

The data for these blends (Tables 12, 13 and 14) show that the H2 is being consistently consumed. The common features in these blends are the high level of CO present together with the critical amount of H2 (brought about by stage 1 catalyst). The resulting critical amount of H2 does not suppress the formation of NO, thereby allow the NO and CO catalytic reaction to manifest itself over stage 2 catalyst.

Table 13 -Fuel blend 11 b Temp.u/s 431 C, To amp. d/s 688 C, LV 10 r n/s, Pressure 333 kPa Measured at Components Calculated vol.% downstream of catalyst N2 58.4 H2 13.0 9.4% : CH4 1.6 1.1% NH3 0.24 124ppm H2O O CO2 7.2 8.4% CO 17.3 17.2% O2 2.4 0.78% : NO O Oppm Table 14 - Fuel blend 8b Temp.u/s 431 C, T emp. d/s 686 C, LV 9.5 m/s, Pressure 331 kPa Measured at Components Calculated vol.% downstream of catalyst N2 63.0 H2 10.4 7.6% CH4 1.7 1.0% NH3 0.26 243ppm H2O o CO2 3.5 5.6% CO 18.5 17. 4% O2 2.5 0.8% NO O Oppm \S C 5 a, - I c Q c Àfi s s o 3 o - s Qs 3.C _ C s tt al s I4) ,,, o. w I C a) al Z o0, Àc o s I O It I E s o '8 E3 ' Z 3 E s _ _ c =3 E =a) E - Z I s s 00 -: s, 2 s N 0 Q C tU E N C S G. 03 o S S C D >' (: Z, = N = (] I s a) s c E s s Q s.0 o 3 Q 0 0 , C m Q cn C o x O 2 -- N. À- C - 2 ' 0 a O O 3 2 < = 2 3 s w E s s 43 -

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g mm 4 u, E=)y Y-c _ 0 a) 0.- a' 0 c 3 o I 8 <, I z c E E. . o a) z o o = U) U) tD -t 4, 3 4', C: _ = aim 1 1 __ \ =0, r--4-. _ 4X = 1 () 43 Id ---_ ago talc O I' ii 3 Q en= ji _. ! 41= ace 1 Y il . jet,'o)= e '' 2-a) =' I u= a._ a, ', E o N E E ' E E o

E _ _

4, 2 0 n to 0 I E 0 43 - E c 2 ' (: g O -m O O ED 8 o i o À I E Example 3 - A typical sizing and layout of the catalytic reactor For 6 combustors Pressure casing Fuel mass flow= 3.22kg/s / For 6 P=12.8bar / combustors T= 660 | Air= 1.020kg/s 1 i' I \. Vol flow fuel + air 1 Stage 1= 0.704 m3/s Air=0.462kg/s | Mixture temp= 653 K For stage 2. ,, Mixture density= 6.029 kg/m3 Vol after stage 1 at À. ..

(70% H2comb.)= 1.32 m3/s À, . m. À. Catalyst for stage 1 Adjabatictemp.= 1274 K H2 H2- 3.7% I S' ning Dia = 0.22 m O2=0.26% etc. I to iitres LV 18 Sm/s -Depth= 0.26 m I Ghsv 2s300 h' (actual) X-area= 0.038 m2 Vol before stage 2 when mixed. _ _. Vol= 0.01 m with more air (0.462kg/s at _ 623 K)= 1.42 m3/s7 \ 02= 2.13%/ \ Mixture temp= 1248 K Mixture density= 3.32 kg/m3. __ Vol after stage 2= 1 512m3/s NH3 + O2 NO Catalyst for stage Adiabatic exit temp.= 1533K | NO + CO N2 + CO2 2 H2= 2.74% 1 S9e 2 _ Dia = 0.31 m 02= 0 0097% 1 20 litres LV 18m/s _ Depth= 0.26 m CH4= 1 23% Ghsv 255000 h- ' (actual) X-area= 0.075 m CV of remaining fuel - 3.3MJ/kg Vol= 0.02 m Add remaining air= 10.95 kg/s / At 623 K for name combustion _ \ / _ Mixturetemp. before combustion= 94_ \ / _ Mixture density= 4.66 kg/m3 \ / Fuel + air vol% composition without any front end processing: Inlet fuel gas to flame 6 combustors via 6x 2" H2: 3 54 /O Fuel + air composition vol% after mixing with H2O: 2.14% combustion air CH4: 0 423% H2 0.864% CO4 59% O2 14.4% CO2 1 91 /0 CO 3 74% Mixture temp: 632 K CO2: 2.92% Mixture density: 6.85 kg/m3 NH3j 0.0220% Adiabatic exit temp: 1395 K Mixture temp: 947 K Total mass flow for 6 Mixture density: 4.66 kg/m3 combustors: 15.66 kg/s Adiabatic exit temp: 1411 K Total mass flow of fuel and air for 6 combustors= 15.66 kg/s - 18 References 1. 4th FWP project ref JOR 3970157, (1997-1999) 2. 5th FWP project ret ERK5-1999-002O, (2000-2003) 3. L Lietti, G Ramis, G Busca, F Bregani, P Forzatti, Catalysis Today 61, 187-195, (2000) 4. 'Development of Improved Stable Catalysts and Trace Element Capture for Hot Gas Cleaning' DTI/ETSU/Clean Coal Power Generation Group, Project Profile 178, (1996) 5. E M Johansson, S G Jaras, Catal Today 47, 359, (1999) 6. B Goldschmidt, N Padban, M Cannon, G Kelsall, M Neergard, K Stahl, I Oderbrand, 'Ammonia formation and NOx conversions with various biomass and waste fuels at the Varnamo 18 MWth IGCC plant, 5th Conference on Progress in Thermochemical Biomass Conversion, Tyrol, Austria, 17-22 September 2000 7. UK Patent GB 2343178, 'Catalytic conversion of NH3 to N2' 8. L Lietti, G Groppi, C Cristiani, P Fotzatti, 'Ammonia oxidation during the catalytic combustion of gasified biomass fuel over Me- hexaluminate(Me=Mn,Co,Fe,Ni,Cr) catalysts', 4th International Workshop on Catalytic Combustion, San Diego, April 14- 16, (1999) 9. G Kelsall, M Cannon, 'Combustion of Low Heating Value Gas in a Gas Turbine', Power Production from Biomass II, Espoo, Finland, March (1995) 10. P Simell, E Kurkela, P Stahlberg, J Hepola, Catal. Today, 27, 55-62, (1996) 11. J Leppalahti, Fuel, 71, 1363-1368, (1995) 12. E Rosen, C B Bjornbom, Q Yu, K Sjostrom, A V In Bridgwater and D G B Boocock (eds): 'Developments in Thermochemical Biomass Conversion', London, Blackie Academic & Professionals, 817-827, (1997)

Claims (9)

1. Claims 1. A process for the catalytic cracking of NH3 contained in

   gasified fuels, whose origin may be coal, biomass, municipal waste, heavy oil, refinery residues and all industrial waste that has fuel value and that liberates NH3 during the gasification process; thereby mitigating against the formation of NOX in the combustion process
2. 2. A process that takes place on multiple catalyst stages in a sequential fashion
3. 3. A process that claims the catalytic oxidation of H2 to a critical amount so as to promote the oxidation of NH3 to NO
4. 4. A process that claims the catalytic oxidation of NO with CO to form N2
5. 5. A process that claims the formation of entity -CONH2 which promotes the selective catalytic reaction SCR
6. 6. A process that claims to operate from atmospheric pressure up to 20 bar and temperature ranging from 600 C to 900 C
7. 7. A process that claims the catalytic combustor design and the mixing arrangement that appropriately prepares the fuel and air mixture for the downstream catalytic reactions
8. 8. A process that claims the catalysts formulations, composition and lay out for both stages 1 and 2
9. 9. The claims of the process is explicitly shown in examples 1, 2, and 3 where all the above claims occur sequentially and simultaneously to achieve the conversion shown in Table 1 and better.