Low NOx burners in Japan

LOW NO x BURNERS IN JAPAN NIPPON FURNACE KOGYO KAISHA LTD. YASUO HIROSE RYOICHI TANAKA NOx regulations in Japan In May 1973 the Japanese government set an environmental quality standard for nitrogen oxides (NO2) that is more stringent than that in any other country of the world. The standard required that ambient concentrations of NO2 to be kept below 0.02 ppm in a daily average of hourly values. The Japanese standard was about 5 times more stringent than that of the United States Standard; 0.05 ppm yearly average, which is close to 0.1 ppm daily average. Fig. 1 shows that the average N02 concentration at 15 ambient measurement points (Tokyo, Osaka, Yokohama, etc.) was 0.025 ppm in yearly average, which was 2.5 times higher than the ambient standard for 1973. In order to reduce these ambient N02 levels below the ambient standard (0.02 ppm daily average) in 5 or 8 years from 1973, it was considered that a special effort had to be done; it meaned that most of the combustion equipments had to be equipped with a flue gas denitrification plant. A flue gas denitrification plant, however, is very expensive; 1,000,000,000 Yen (400,000 dollars, $1.0=¥250.-)/ 100,000 Nm3/hr for installation, and 72,900 Yen (290 3 dollars)/10,000 Nm as running cost as of 1975. k By the way, an oil crisis attached Japan which is a country with small energy resources in 1973. Japan made an effort to save energy in all fields including, heavy, light and domestic industries. Of course, there was an in case of opinion that energy should be saved ,}&?> reducing N0 X ?by ow NO* burner w.'thou.t A a flue gas denitrification plant except for special big combustion systems, sintering furnace and nitric oxidation acid plant. , , , .. , ^ ./ it Ms the bluest reason for the cAianje of That opinion gained major supports and; Japanese environmental quality standard %#mfrhnngprlfrom 0.02 ppm to 0.04 - 0.06 ppm in daily average in July 1978. Thus, as compared with the fact that, the previous environmental quality standard was achieved only at 8% of N0 2 measurement points in Japan in 1975, the new standard f has been attained by more than 92% (see Table 1). An exhaust flue gas regulation of NO x was set progressively for wider variety of equipments and more stringently than the first regulation of August 1973 up to the fourth regulation formed in August 1979 (see Table 2) which is thought to be the last regulation. I think it easy to fulfill the regulation by using combustion technology. The most polluted area will be controlled by a "Reduction of total quantity" program. In that case, some of be the equipments in the area need to^equipped with a flue gas denitrification plant. The corrected N0 X concentration is calculated by the equation below. [N0X]C = Itlofil X [NOx]m (1) [N0X]C: corrected N0X, [02]n: standard 02% for correction [N0x]n: measured N0X, [02]m: measured 02% on dry base The mechanism of N0X formation There are two routes of N0X formation; thermal N0X and fuel N0X. Thermal N0X The mechanism of thermal N0X formation attributed to reaction between N2 and 02 in the air is that of Zeldovich. 4°2 = 0 (2) 0 + N2 ^^: NO + N (3) N + 02 :=" NO + 0 (4) If we neglect the reverse reaction in formulae (3) and (4), formula shown below is obtained. ^&=k[N2][02]1/2 (5) where k is given in the following formula by Zeldovich. k = 3 x 104 exp (-129,000/RT)CC1/2mol"1/2S_1 ...(6) So, we can understand the following facts about thermal ^s N0X from formulae (5) and (6): (i) NO(NOx) increases exponentially with temperature (see Fig. 2). (ii) NO changes with 02 (ratio in the air) (see Fig. 3). (iii) NO increases with residence time (see Fig. 4). Fuel N0X Fuel N0X came to be closely watched later than thermal N0X. Petroleum and coal fuels include nitrogen as pyridine, indole, quinoline, carbazole, etc. (see Fig. 5). Table 3 shows nitrogen content in a typical Japanese fuel oil. If all the nitrogen content is converted to N0X, N0X concentration in flue gas is about 155 ppm (corrected to 0%O2) for heavy oil about 200 ppm (corrected to 0%O2) for coal per 0.1 wt% of nitrogen content. But actually, all nitrogen doesn't change to NOx. Fuel N changes to NOx and N2 through intermediate substances I (NH, NH2, NH3, HCN, CN ) Fuel N - So we call the changing rate from fuel N to NOx as the "NOx conversion rate". This conversion rate is strongly . influenced by air ratio, nitrogen content and heat loss (see Fig. 6 and 7). Low N0X burners in Japan There are many low N0X burners which are developed and commercialized by Japanese burner makers, gas companies and iron steel companies. The number of types of low N0X burners available in Japan will be more than 20. We now classify these burners into 4 groups by the principle. (i) Flame cooled after rapid mixing (ii) Self-recirculation type (iii) Two stage combustion (iv) Off stoichiometric Flame cooled after rapid mixing NO formulation speed is slower than main combustion speed (see Fig. 8). If rapid mixing of air and fuel is possible and the flame is cooled after main combustion reaction, it is possible to reduce NO formation. This type of burner is mainly applied to a water cooled boiler. [NKF-TRW burner] Fig. 9 shows an NFK-TRW burner. - 5 - Fig. 10 shows NO x emission from the NFK-TRW burner of a packaged boiler. Fig. 11 shows temperature distributions of NFK-TRW burner and a conventional burner in a test furnace. [IHI- Split .. flame burner] This burner is probably the first low NOx burner ever developed in Japan. Fig. 12 shows the burner top of mechanical atomizer with 4 slits for dividing the flame into 4 parts. Fig. 13 shows NOx emission from IHI-divided flame burner and others. Self recirculation This burner type uses entrainment force of combustion air and/or fuel jet momentum. Comparatively low temperature combustion gas is entrained by air and/or fuel jet. Thus, it can decrease maximum flame temperature, and so it's possible to control NOx emission. [Daido Steel low NOx burners] Fig. 14 shows Daido Steel R and RO burners. Fig. 15 shows NOx emission from Daido RO burner. [Osaka Gas XB burner] Fig. 16 shows Osaka Gas XB-burner. Fig. 17 shows NOx emission from 8 t/hr Steam boiler with XB-burner. - 6 - [Chugai -* NPL burner] Fig. 18 shows Chugai - NPL burner. Fig. 19 shows N0X emission vs. furnace. [Sumitomo Steel - RSNT burner] Fig. 20 shows Sumitomo Steel - RSNT burner. Fig. 21 shows NOx emission vs. furnace temperature. Two stage combustion The combustion air is injected in two stages; In the first stage, air is put in near at burner nozzle, and in the second stage, air is put into the end of the combustion chamber. Insufficiency of air (lack of 02) in first-stage combustion and slow combustion in the second stage keep both flame temperature and conversion rate of fuel NOx at low level. This will be useful for both thermal and fuel NOx control. [Two-stage combustor] Fig. 22 shows Fig. 23 shows the effect of two-stage combustion on NOx emission. [TZ burner] Fig. 24 shows a two-stage fuel injection combustor (TZ burner). - 7 - Fig. 25 shows NO emission vs. furnace temperature. [NFK-SRG burner] Fig. 26 shows the principle of NFK-SRG burner. Fig. 27 shows N0 X emission and N0 X reduction rate vs. air ratio. Type of off stoichiometric Theoretical N0 X formation vs. air ratio is shown in Fig. 28. A peak of N0 X emission substantially represents a stoichiometric air ratio, and both fuel rich and fuel lean conditions lead to lower N0 X emission than stoichiometric point. So if fuel rich and fuel lean flames are mixed after each flame is formed by each burner nozzle, it is possible to reduce N0 X emission (see Fig. 28). [MHI - off stoichiometric burner] Fig. 29 shows MHI - off stoichiometric burner. Fig. 30 shows NO x emission of MHI burner with flue gas recirculation. [Volcano - low NOx burner tip] Fig. 31 shows Volcano - low NO x burner tips. Fig. 32 shows NO x emission of low NO x burner tips. [NFK - pulse combustor] Fig. 33 shows the principle of NFK - pulse combustor. Fig. 34 shows NO x emission from NFK - pulse combustor. [NFK «•» CLN burner] Fig. 35 shows the principle of NFK - CLN burner. Fig. 36 shows N0X emission from .NFK - CLN burner. 4. Trend of low N0X combustion Oil crisis has provided a momentum for using residual oil and preheated air by flue gas heat recovery. It is a problem how to reduce N0X emission under these circumstances. Residual oil has usually a high content of fuel N, so it is important to keep low conversion rate of fuel N0X. Fig. 37 shows the two stage combustion test equipment for testing fuel N0X conversion rate. Fig. 38 shows the test results. N0X emission is reduced but NH3 and HCN increase when the first stage air goes down gradually from stoichiometric value without secondary air. If the secondary air is injected after the first stage combustion, NH3 and HCN will change to N0X. So N0X emission will increase in exhaust gas after second stage combustion (see Fig. 39). But we found out the minimum fuel N0X conversion rate will be at about X(air ratio) = 0.8. Fig. 40 shows fuel NOx vs. lry air ratio. You can see conversion ratio is almost zero at X*= 0. 8. By the way, preheated air pushes up NOx emission level as shown in Fig. 41 for conventional burners, but NOx - 9- emission level slightly changes in case of two-stage combustion. For example, Fig. 42 shows comparison of N0X emission in the case where preheated air is used for NFK - SRG burner (Fig. 26) and conventional burner. N0X emission increases greatly for conventional but slightly for NFK - SRG burner when preheated air changes from 30°C to 400°C. Fig. 43 shows that the maximum flame temperature for 30°C and 400°C combustion air temperature hardly changes in the case of NFK-SRG burner combustion. I believe that two staged combustion type burner is a promising low N0X burner, because it is possible to control the fuel N0X and N0X emission in preheated air combustion. - 10 - (ppm) 0.03 0.027 °v2 28 0.027 0.025 OC CO M 0.02 0.026 0.026 0.022 0.021 -m CO 0.01- 1970 Fig. 1 71 72 73 74 75 76 77 78 (Year) NO£ yearly average concentration at 15 measurement points (according to Japanese EPA) Table 1 Environmental NO2 (yearly average) in 1978 (according to J. EPA.) Number of NO2 measuring points Percentage 0.06 ppm 75 7.6% 0.0A ^ 0.06 ppm 233 23.8% Under 673 68.6% 981 100.0% Over 0.04 ppm Total - 11 - Table 2 4TH NOx EMISSION REGULATION STANDARDS (AUG. 1978) issued by JAPANESE EPA Type of . installation Fuels Applicable capacity of flue gas (Nm3/h) Boiler Solid 130 lOOxlO3 to 500xl03 100 130 40xl03 to lOOxlO3 100 130 lOxlO3 to 40xl03 130 150 5xl03 to lOxlO3 150 150 under 5xl03 150 150 over lOOxlO3 400 480 40xl03 to lOOxlO3 400 480 lOxlO3 to 40xl03 400 480 400 480 under 5xl03 400 480 over 500xl03 130 180 lOOxlO3 to 500xl03 150 190 40xl03 to lOOxlO3 150 190 180 230 180 250 5xl03 to Liquid lOxlO3 5xl03 to lOxlO3 under 5xl03 100 160 3 130 170 lOxlO3 to 40xl03 130 170 5xl03 to lOxlO3 150 170 180 200 100 170 40xl03 to lOOxlO3 100 170 10xlOJ to 40xlOJ 130 180 5xl03 to lOxlO3 150 180 under 5xl03 180 200 over lOOxlO3 40xl0 Metal heating furnace 3 to lOOxlO under 5xl0 3 over lOOxlO3 Oil heating furnace - «. 02 content in gas (%) , New instal- Existing installa- f StaWard 0^ lation tion \\or cotred.o 60 over 500x103 Gas NOx emission in ppm Cement kiln - lOOxlO3 or more under lOOxlO3 250 350 480 480 Incinerator - 40X10-3 or more under 40xl03 250 700 300 900 5 6 * 4 11 6 fe 10 12 15000 8. - o •H •u CO r-l 10000- •U C 0) u c o o •H cP 5000^3 i 3 cr w 1000 500 1000 1500 2000 Temperature (°C) Fig. 2 Temperature vs equilibrium NOx concentration in air • # B a c o •H •U CO >-J •u C ai u c o a s 0.6 1.4 1.8 Air ratio Fig. 3 Air ratio vs N0 X formation . (parameter: residence time) - 13 - IO-"- jo-* • icr* in-*. i 10 IO*- Residence time (sec) Fig. 4 Residence time vs NOx formation (parameter: temperature) Pyridine group Indole group Fig. 5 Typical nitrogen compounds in crude oil - 14 - Table 3 N content in Japanese fuel oil N content Kerosene A heavy oil 0.01 ^ 0.03 wt% B heavy oil 0.10 % 0.15 wt% C heavy oil 0.20 ^ 0.28 wt% 100 80 60 ,->*%'T5T " '0~~30% * 0 I trs'^-~~"~ 0-30% I /Ijl I I N wt% 40 20 ! !/iiiiL- £====& ill, $/* s*~ 0 ^n0/ "' //// /],'tS,--// // J j /' * //VA 0.6 0.8 r \' t 1.0 1.2 i \ 1.4 1.6 Heat Loss | ? 1.8 2.0 Air ratio Fig. 6 Fuel NO conversion rate (by simplified calculation) - 15 - 50 40 • o <: o 0 N A N D N tfN 1 °2 = = = = 0.2% 0.6% 1.0% 1.4% 1 3 2 IN GAS, % Fig. 7 02 v s Conversion ratio (results at test furnace) CO U c o •H •u CO u c <u o c o o o Fig. 8 Concentration change in CH^ - A I R mixture - 16 - Thin annular flame Heat \ radiations- Recirculation flow Fuel gas Recirculation flow Fig. 9 NFK-TRW burner c0| A heavy oil (0.03%N) Room air temperature 380£/h (100% load) 70 B a. o 6^9 60 50 40 d) •U O <v u u Oo u 30 20 10 1.0 1.1 1.2 1.3 1.4 1.5 Air ratio Fig. 10 N 0 X data of NFK-TRW burner - 17 - i^o^to^c^ Flue gas temp. 777°K uonv. burner ^ J ^ ^ 1 1 0 0 K Fig. 11 Comparison of temperature distribution in NFK-TRW and conventional burner combustions e'2 Nozzle Slit Fuel oil spout direction Burner tip detail Divided type tip , Slit Nozzle Fig. 12 IHI- Split flame type oil tip - 18 - Heavy oil* Fuel 4,000 Fuel flow rate (//h) Condition of fuel atomizing • Condition of combustion air Fuel oil pressure of standard atomizer (kg/cm2g) Pressure atomizer Feed oil pressure Return oil pressure 54 32 Steam atomizer (with 8 nozzles) Feed oil pressure Steam pressure 8.0 9.5 Temperature of fuel oil ( ° Q 80 Excess air ratio 1.2 Normal temperature Combustion air temperature at burner inlet 28 Air velociy at burner throat (m/sec) •: Nitrogen content =0.22 w t % Smoke concafltrotion * (Note) 0 : Standard atomizer (pressure atomizing) # : Standard atomizer (steam atomizing) • : In Bacharach smoke number Fig. 13 NOx emission at IHI-Split flame burner - 19 - AIR AIR (A) R TYPE (B) RO TYPE Fig. 14 Daido Steel Low-NO x burner 150 1 1 1 » ROTARY OIL BURNER (OIL-PRESSURE ATOMIZING) 100 OIL-PRESSURE ATOMIZING 8 CL OL a 50 RO TYPE BURNER A <* ..*r % .9 1.0 STEAM ATOMIZING 1.1 1.2 1.3 AIR RATIO o • sfio KB XI, L Xi 4 ir^v ?£ j „** 4-J^/fr HEAVY OIL (GRADE A, 103-113 Z/hr * * KEROSENE (100 £/hr) Fig. 15 Effect of RO type burner - 20 - _ Air 4 r. Combustion flue gas L~_S HI i Fuel gas Fig. 16 Osaka Gas XB-burner 12 60 I - SO 10 a. CN o _____ 8 40 0) J-i CJ <D J-I J-I o o o _U # CU t 30 CO to A $y v» 3 NOx VV \§. _ * • ' I* «h • 4 B>5 CN 1U 2 20 40 60 80 100 Load (%) Fig. 17 Concentration from N0 X 8 t/h steam boiler with XB-burner (city gas) - 21 - o^ r* Burner block Pilot burner Air Oil Recirculation Fig. 18 Chugai NPL burner ki 50 B a a CN Fuel kerose ne 40 O fr* 30 •a <u u CD J-i J-i O oo 2*0 < ^ / ^<T / 55£/h ^ ^ 50£/h 10 30£/hJ 150/h : " . • V 0 800 -900 1000 "J!DO'•-•1200 -1300 - • - • • Furnace temp. (°C) Fig. 19 Furnace temperature vs N0 X (NPL burner) - 22 - Air Swirl air jet #u/rv Fig. 20 4//t ^7AC/^J^ Sumitomo Steel RSNT-burner Conventional burner (C-heavy oil) O- HSC-heavy oil (N: 0.23 wt%) g = b==^H" Ar ^MINAS-heavy oil (N: 0.17 wt%) • 900 1000_ 1100 1200 1300 Special-oil (N: 0.06 wt%) 1400 Furnace temperature (°C) Fig. 21 NO x vs furnace temperature (RSNT-burner) - 23 - 2nd air lry air Q 0 Main combustion zone "bust ion v \ Wind box Fig. 22 Two stage combustor C-heavy oil (0.206%N) , 1,740//h x .^x ^,2x/7^' B 1,300 //h CN o <r o 4-1 <u U o 0) J-I J-I o o X o 2 0 10 20 30 40 2nd air flow x 100% Total air flow Fig. 23 Effect of two stage combustion - 2k - Furnace wall Secondry Fuel (60-40%) Primery Fuel (40-60 96) 3^sjn=1.6-2.4|v?: m = 1.05-1.2 iff Combustor Fig. 2A Two stage fuel injection combustor (TZ burner) 9100 a P. CN ° 80 rH rH 0 r -A-Heavy oil - A *•* -60 <U 4-1 o 2 4U - C3H3 -- o a - z 20 0 - " '1 1 Kerosene 8CiO 10 00 12 00 1'300 Furnatze temp . (°C) Fig. 25 NO vs furnace temp. (TZ burner) - 25 - /GASIFICATION GAS* 1 CO, H 2 RICH ' RE-COMBUSTION GAS COvH„0-N2-02 GASIFICATION REACTION C + o2-co2 C02 • C ^ 2 C 0 COMBUSTION PRODUCTS C + H 2 0^rCO + H 2 Qnlln + mHgO^mCO + ^ E SECONDARY AIR ' (02-N2) FUE CmHn Fig. 26 NFK-SRG burner N0x vs AIR RATIO. SRG BURNER AND TANDEM BURNER © ~ 350, * ~ 200 o o 2= 1 j- B FUEL OIL 105 g/hr 1.0 1.1 «j NO 1.0 Fig, 27 H ~~T 1.1 1.2 1.3 1.4 AIR RATIO, X 1.5 REDUCTION RATE, SRG vs TANDEM 1.2 1.3 1.4 AIR RATIO, X 1.5 NO x and NO x reduction ratio vs air ratio (NFK-SRG burner) - 26 - ^ Fuel lean E Q. K O 2 Fig. 28 Concept of off stoichiometric combustion jf - 27 - AIR RICH MIX '=frn '/M A WXER t B "V- IS 0 . ^„- i?;i i) 0 ^1 ^3 0 | TO FUEL RICH MIX Fig. 29 MHI off-stoichiometric burner CM o en O o E o. GL 0 10 20 30 FLUE GAS RECIRCULATION RATIO, % A CONVENTIONAL BURNER, 2 t/hr o MHI L0W-N0x BURNER, 2 t/hr . ° MHI L0W-N0x BURNER, 8 t/hr Fig. 30 NOx emission at MHI Low NOx burner with flue gas recirculation - 28 - Oil Steam Fig. 31 Volcano - Low NOx burner tips B-Heavy oil NO* reduction //•N / 5-5 40 o •H 30 « i 9 J-I Uto .J 20 g: 6 •H io 3s -• 3 oil off st 0 <u_ J-I X o a Fig. 32 N0 X emission, N0 X reduction rate and smoke number at Volcano Low NOx burner tip - 29 - 0 0) E 3 C a E W ratio o Air (d)Fuel supply (a) Steady air flow Fuel V • a o°o o o^o o o o o o (e) R a m e moving (b) Fuel supply O 5 o o o o o o o o o o fo o o o o o o o o o o o © o o o o o o ° ° o o O O O O P o o o o \p o o o o o o o fo o o o o o o o \0 O o ° o o o o o o o oc o o o o o o oc (c) Fuel supply stop Fig. 33 (f^Conventional flame Principle of NFK-pulse combustor 90 E QOL City gas Air temp. 280 °C Tube temp. 1000 °C 80 o 70 2 60 D S.50 X O 40 30 10 20 30 40 50 60 70 Setting pulse frequency Hz Fig. 34 - 30 - Pulse frequency vs NOx emission 80 90 100 (Fuel lean) (Fuel rich) %\JM^ (Flue gas) (Scrambling entrainment) Fig. 35 Principle of NFK-CLN burner 130 . y° 0 o a n/ _ 120 - . o 71 /o 110 P° o o.faa 0° 6 . 100 a /•^ CN O , 80 Conventional ° ° °/\ > 'Burner o /o 300T/h o/ o COG + BFC 4 000 Kcil/Nm1 / 70 °/o a 90 O &*s / NFK-CLN Burners are put on heating zone only X 13 4J O 01 J-I o u X O !S 60 / SSV/«"K / 50 X ^ y * X*K * / V -^ 1 40 / / C^ " - < >" /** 30 - X'.« / X x x" 20 1 r 1 i 2 ^ • Vrediction of all NFK-CLN Durners • r 3 1 J 4 5 1 6 ! 7 f 8 9 Flue gas O2 % Fig. 36 N0X emission at the actual iron heating furnace - 31 - m *-AIR 2 T.C.and Sample. AIR1 FUEL 400 Fig. 37 r Two stage test combustor 0.6 0.S 1.0 1.2 AIR RATIO A, Fig. 38 - 32 - lry air vs NO x , HCN, NH3 emission BOD i BOO r 500 400 300 200 100 06 0£ Air ratio X (without fuel N-NH3) Air ratio X (without fuel N) Fig. 39 NOx emission at two stage combustion without fuel N and with fuel N 300 200 B a ao* 2 a) P as 0.8 10 1.2 lry air ratio X Fig. 40 - 33 - Fuel NOx vs lry air ratio 0> u 3 4J CO u Cu + B TO X o LOO Combustion air temperature (°C) Fig. 41 NOx increase vs air temperature - 34 - 600 PREHEAT AIR TEMP • o 35 °C A A 250 e °400 FUEL^GAS CONVENTIONAL FLAME 400 Q_ CL x O 200 SELF RECIRCULATING FLAME 1.0 1.1 Fig. 42 . 1.2 - 1.3 FXCFSS AIR RATIO 1.4 1.5 Comparision of NOx emission between NFK-SRG burner and conventional burner at preheated air A Conv B. 35'L O Ret. B 35'C C Rec B. AOO'C 1600- u CL 1 500 - E O E 1400<T3 1300 1 Fig. 43 2 3 Furnace Length 4 m Temperature distribution along furnace axis - 35 - References 1) Japanese E.P.A report, I98O 2) Kato, Nagata and Himi, "Challenge to NOx" Japanese Energy Technical Association, 1976 3) Tsuji, Tsukada and Asai, IHI Engineering Review, Vol. 6, No. 2, 1973 k) Matsuo and Yoda, Nippon Steel Technical Report, No. 300, 1980 The 5) NOx Control Association Report, Japan LP (r<HS Association, 1979 6) Hirose, 4th Members Conference, 1976 7) Hirose and Kannari, 5th Members Conference, 1978 8) Hirose and Hasegawa, 6th Members Conference, I98O 9) Hazama and Sadakata, 45 Symposium of Japanese Chemical Engineering Association, I98O - 36 -