CN101187475A - Method for reducing elemental mercury, nitrogen oxide discharging for coal-fired boiler classified recombustion - Google Patents

Abstract

The invention discloses a method of lowering the discharging of elemental mercury and nitrogen oxides in flue gas when a coal-burning boiler reburns in grading, which comprises firstly, selecting CH4 gas as grading reburning gas, and simultaneously selecting the mixed gas of CH4 and NH3 as second-grade reburning gas, secondly, feeding reburning fuel into the coal-burning boiler in two grades, wherein feeding the CH4 into a reburning nozzle (1), feeding the CH4 and the mixture gas of the NH3 into a reburning nozzle (2), arranging an overhead wind nozzle between the reburning nozzle (1) and the reburning nozzle (2), Q(CH#[4)1]: Q(CH#[4)2]= 0.01-0.02, Q(CH4#[2]: Q(NH#[3]= 1:1, thirdly, combining with a wet process of FGD for application. The invention transforms zero-valent mercury into divalent mercury which is easily adsorbed through fly ash, serous fluid and the like, and the purpose of simultaneous removing of a plurality of pollutants can be achieved through combining with the current wet process of FGD.

Description

The coal-fired boiler classified method that reduces simple substance mercury, discharged nitrous oxides in the flue gas when firing again

Technical field

The present invention relates to a kind of method that reduces the gas pollutant discharging that coal-burning boiler when burning produce, relate to a kind of in particular in the coal-fired boiler classified method that reduces simple substance mercury, discharged nitrous oxides in the flue gas when firing again.

Background technology

Problem of environmental pollution has become the focal issue that the whole world is paid close attention to now.Coal combustion is the greatest contamination source of causing NOx and Hg to pollute.Electrical production mainly depends on coal-fired power plant at present, and especially Chinese, its ratio accounts for 75% of gross generation, we can say that the coal-burning power plant is the concentrated area of coal consumption and NOx and Hg pollution.Particularly because a large amount of burnings of coal, the mercury total amount of overflowing from fire coal every year in the whole world reaches more than the 3000t.Mercury in the coal owing to high temperature gasifies, along with the cooling of burning gases, interacts with other combustion products and has produced oxidation state mercury and particle mercury in coal combustion process, and three kinds of forms are called total mercury, and in the majority with gaseous mercury.Simple substance mercury is volatile, and solubility is low, the toxicity height, chemical property is stable, is difficult for reacting with other chemical substances, the route of transmission is wide, in environment the time of staying long, be difficult for removing.A large amount of mercury are by the also possible polluted-water of dried wet deposition, and biological methylation reaction back forms the methyl mercury of severe toxicity, this organic mercury toxicity is the highest, can injure brain, and more stable, can enrichment in ocean, fresh water lake and aquatile, the half-life that stops in human body reaches 70 days, even dosage seldom also can be accumulated intoxicating, human body is caused great harm.

Present situation at the coal-fired process mercury pollution, researchers have proposed various control methods, comprise sorbent injection method, fixed bed filtering method, wet flue gas desulfurization associating removal of mercury method etc., preceding two kinds of adsorbents that all need efficient cheapness, be commonly referred to as the adsorbents adsorb method, the third then needs oxidant is divalence mercury with the simple substance mercury oxidation in the flue gas.Because the simple substance mercury shape is stable, from flue gas, directly remove relatively difficulty of simple substance mercury, be discharged into and cause in the atmosphere that air pollutes on a large scale, and divalence mercury easily is adsorbed on and is collected by various dedusters on the lime-ash in the flue gas, it is fairly simple that it gets rid of technology, so,, then can effectively reduce the mercury pollution of fired coal combustion to environment if the simple substance mercury after the burning can be converted into divalence mercury as far as possible.Simultaneously, the NOx of minimizing fired coal combustion generation is compound polluted also is one of emphasis of efforts at environmental protection person's research all the time.

Summary of the invention

Technical problem to be solved by this invention provides and a kind ofly nonvalent mercury is converted into more easily mercuric method for absorption such as flying dust and slurries coal-fired boiler classified when firing again, thereby reaches the purpose that multiple pollutant removes simultaneously.

The technical solution used in the present invention: the coal-fired boiler classified method that reduces simple substance mercury, discharged nitrous oxides in the flue gas when firing again comprises the following steps:

A. select CH for use ₄Gas is classification combustion gas body again, selects CH simultaneously for use ₄And NH ₃Mist be secondary combustion gas body again;

B. reburning fuel branch two-stage is sent in the coal-burning boiler, wherein fires spout (1) again and sends into CH ₄, the spout (2) that burns is again sent into CH ₄And NH ₃Mist is furnished with the overhead wind snout firing between spout (1) and (2) again, and the ratio of each spout spacing is to fire spout (1) height h again ₁: overall height H=0.01～0.5, overhead wind snout height h ₂: overall height H=0.01～0.2, fire spout (2) height h again ₃: overall height H=0.01～0.2, fire the CH of combustion again that spout (1) sprays into again ₄Amount is Q _{(CH4) 1}, fire the CH that spout (2) sprays into again ₄Amount is Q _{(CH4) 2}, fire the NH that spout (2) sprays into again ₃Amount is Q _NH3, Q _{(CH4) 1}: Q _{(CH4) 2}=0.01～0.20, Q _{(CH4) 2}: Q _NH3=1: 1;

C. the associating removal effect that can reach pollutant with the wet flue gas desulfurization method use in conjunction is fired in above-mentioned classification again, reduces the discharging of simple substance mercury, nitrogen oxide in the flue gas.

Beneficial effect of the present invention: the present invention is converted into the divalence mercury that more easily adsorbs for flying dust and slurries etc. to nonvalent mercury, thereby reaches the purpose that multiple pollutant removes simultaneously by the use in conjunction with existing wet flue gas desulfurization method again.Natural gas reburning denitration mechanism is to have generated NO to run into hydrocarbon root CHi and imperfect combustion product C O, H in principle ₂, the reduction reaction of NO during CnHm, can take place in C.The overall reaction equation is:

4NO+CH ₄→2N ₂+CO ₂+H ₂O

2NO+2C _nH _m+(2n+m/2-1)O ₂→N ₂+2nCO ₂+mH ₂O

2NO+2CO→N ₂+2CO ₂

2NO+2C→N ₂+2CO

2NO+2H ₂→N ₂+2H ₂O

NH ₃Denitration by refueling mechanism be: NH under the high temperature ₃Can carry out the SNCR reaction with NOx in the flue gas, generate N ₂, help denitrogenating, react and be: 4NH3+4NO+O2=4N2+6H2O

The natural gas reburning process can be analyzed from the following aspects the mechanism of action of Hg:

In the natural gas reburning process, under the aerobic situation with CH ₄And NH ₃Carry out chemical reaction, can produce material: 2CH such as HCN ₄+ 3O ₂+ 2NH ₃=2HCN+6H ₂O

HCN is not very stable, can be converted into other material (as HCNO etc.) under the situation that oxygen exists, but still have small amount of H CN or CN at furnace outlet rear portion flue ^-, their can react with mercury, and oxidation simple substance mercury or fixing divalence mercury make it transform towards helping catching fixing direction:

2Hg+8CN ^-+2H ₂O+O ₂→2Hg(CN) ₄ ^2-+4OH ^-

Hg ²⁺+2CN ^-＝Hg(CN) ₂

Hg(CN) ₂+2CN ^-＝Hg(CN) ₄ ^2-

HgO+4CN ^-+H ₂O＝Hg(CN) ₄ ^2-+2OH ^-

And HCNO also has oxidation to Hg.Meanwhile, CH ₄The H that generates in the combustion process ₂O also helps the Cl in the flue gas ₂, material such as HCl is to oxidation and the capture-process of Hg, thereby the form that helps mercury transforms towards the direction of being convenient to adsorbing and removing.

Description of drawings

Fig. 1 is that sublevel fires schematic diagram again;

Fig. 2 is the trial furnace system schematic.

Fig. 3 single-unit furnace binding schematic diagram

Fig. 4 burner hearth body and sample position sketch

The specific embodiment

Below by drawings and Examples the present invention is described in further detail: the coal-fired boiler classified method that reduces simple substance mercury, discharged nitrous oxides in the flue gas when firing again, comprise the following steps, as shown in Figure 1:

A. select CH for use ₄Gas is classification combustion gas body again, selects CH simultaneously for use ₄And NH ₃Mist be secondary combustion gas body again;

B. reburning fuel branch two-stage is sent in the coal-burning boiler, wherein fires spout (1) again and sends into CH ₄, the spout (2) that burns is again sent into CH ₄And NH ₃Mist is furnished with the overhead wind snout firing between spout (1) and (2) again, and the ratio of each spout spacing is to fire spout (1) height h again ₁: overall height H=0.01～0.5, overhead wind snout height h ₂: overall height H=0.01～0.2, fire spout (2) height h again ₃: overall height H=0.01～0.2, fire the CH of combustion again that spout (1) sprays into again ₄Amount is Q _{(CH4) 1}, fire the CH that spout (2) sprays into again ₄Amount is Q _{(CH4) 2}, fire the NH that spout (2) sprays into again ₃Amount is Q _NH3, Q _{(CH4) 1}: Q _{(CH4) 2}=0.01～0.20, Q _{(CH4) 2}: Q _NH3=1: 1;

C. the associating removal effect that can reach pollutant with the wet flue gas desulfurization method use in conjunction is fired in above-mentioned classification again, reduces the discharging of simple substance mercury, nitrogen oxide in the flue gas.

Embodiment 1

Experimental study is carried out on one dimension coal dust firing pilot system, the whole test system partly is made up of one dimension trial furnace burner hearth body, hot-air system, feeding system, combustion system, heating system, cooling system, dust pelletizing system and monitoring system etc., the sampling and analysing of trace heavy metal element mercury in the coal-fired flue-gas, adopt Ontario method (Ontario Hydro Method), NO in the flue gas _xAnd SO ₂Measurement adopt electrochemical process to carry out flue gas analysis.The burner hearth body is a modular construction, height overall 5m, and internal diameter 300mm can be divided into base and 5 segmentation bodies of heater that structure is identical.Body of heater channel-section steel stent support is used bolting between each section, and takes seal approach.The body of heater overall structure as shown in Figure 2.1. air blast 2. preheaters 3. charging gears 4. burners 5. thief holes 6. gas coolers 7. sack cleaners 8. air-introduced machines 9. chimneys 10. thermometers 11. Pressure gauges 12. valves 13. flowmeters 14. bodies of heater, whole body of heater is followed successively by one section, two sections, three sections, four sections, five sections and base from top to bottom, each section body of heater height is 800mm, and five sections all have the sublevel air port.Each section body of heater is divided into four layers from inside to outside: the inside one deck is the carborundum cover, can bear high temperature; The second layer is a zone of heating, and the centre is connected with resistance wire, is used for the interior air of heating furnace to the temperature of setting; The 3rd layer is muff, can reduce radiation loss; Outermost one deck is the shell of refractory fibre system.Fig. 3 is a single-unit furnace binding schematic diagram.Wherein have thief hole on second section to the 5th section.Have the hole that diameter is 60mm above body of heater, inlet acts as a fuel.Side at base has exhanst gas outlet.The position in burner hearth body and smoke sampling hole as shown in Figure 4.That wherein send in one section air outlet is CH ₄That send in three sections air outlets is CH ₄+ NH ₃Two sections air outlets are the overhead wind snout, send into an amount of air.Testing used coal dust from the coal-burning power plant, is a kind of mixed coal, has all passed through the mechanical disruption and the sieve that shakes before the test.Operating condition of test is that coal dust coal-supplying amount 8kg/h, excess air coefficient are 1.2, primary air flow 15.18Nm ³/ h, secondary air flow 35.42Nm ³/ h, 70 ℃ of exhaust gas temperatures.The form of mercury in coal-fired product is distributed as in this example: gaseous state divalence mercury accounts for 60%, and gaseous elemental mercury accounts for 20%, and the flying dust mercury content is 15%, and the slag mercury content is 5%.Converting 6% oxygen amount, is 300mg/m during the concentration of NO in the flue gas ³, SO ₂Content be 560mg/m ³

Embodiment 2

Testing equipment, the operating condition of test primary condition is identical with embodiment 1, just done certain modification in the combustion process: with calcium sulfur ratio is that 2 ratio is mixed the agstone desulfurization, and spray into natural gas for second section at burner hearth, the 5th section sprays into after-flame wind, the effect of natural gas denitration when investigating the desulfurization of stove sodalime stone, and combined influence.The form of mercury in coal-fired product is distributed as in this example: gaseous state divalence mercury still accounts for 60%; But the gaseous elemental mercury content is almost nil, can ignore; The flying dust mercury content is corresponding to rise to 30%, and the slag mercury content has also brought up to 10%.Converting 6% oxygen amount, is 310mg/m during the concentration of NO in the flue gas ³, SO ₂Content be 450mg/m ³By above two examples as can be seen, by natural gas reburning, the amount that limits the gas spraying inlet and the height ratio between spout and adding limestone desulfurization, nonvalent mercury in the coal-fired product significantly reduces, and the mercury in lime-ash and the flying dust rolls up, and the emission reduction effect of mercury is remarkable; NO in the flue gas, SO ₂Content also reduced about 1/3, removal effect is remarkable.

Above said content only is the basic explanation of the present invention under conceiving, and according to any equivalent transformation that technical scheme of the present invention is done, all should belong to protection scope of the present invention.

Claims (1)

1. the coal-fired boiler classified method that reduces simple substance mercury, discharged nitrous oxides in the flue gas when firing again comprises the following steps:

A. select CH for use ₄Gas is classification combustion gas body again, selects CH simultaneously for use ₄And NH ₃Mist be secondary combustion gas body again;

B. reburning fuel branch two-stage is sent in the coal-burning boiler, wherein fires spout (1) again and sends into CH ₄, the spout (2) that burns is again sent into CH ₄And NH ₃Mist is furnished with the overhead wind snout firing between spout (1) and (2) again, and the ratio of each spout spacing is to fire spout (1) height h again ₁: overall height H=0.01～0.5, overhead wind snout height h ₂: overall height H=0.01～0.2, fire spout (2) height h again ₃: overall height H=0.01～0.2, fire the CH of combustion again that spout (1) sprays into again ₄Amount is Q _{(CH4) 1}, fire the CH that spout (2) sprays into again ₄Amount is Q _{(CH4) 2}, fire the NH that spout (2) sprays into again ₃Amount is Q _NH3, Q _{(CH4) 1}: Q _{(CH4) 2}=0.01～0.20, Q _{(CH4) 2}: Q _NH3=1: 1;

C. the associating removal effect that can reach pollutant with the wet flue gas desulfurization method use in conjunction is fired in above-mentioned classification again, reduces the discharging of simple substance mercury, nitrogen oxide in the flue gas.

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