CN105854548A

CN105854548A - Cement denitration method

Info

Publication number: CN105854548A
Application number: CN201610234416.9A
Authority: CN
Inventors: 廖引家
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-04-15
Filing date: 2016-04-15
Publication date: 2016-08-17

Abstract

The invention discloses a cement denitration method. A selective ncatalytic reduction method is carried out after a selective non-catalytic reduction method is completed. The cement denitration method has the following advantages that the catalyst amount is small, an SCR reaction tower is small in size, space adaptability is high, a denitration system is small in resistance, conversion from SO2 to SO3 is reduced, corrosion damage is reduced, and a reducing agent injection system is simplified.

Description

Cement method of denitration

Technical field

The present invention relates to cement technology field, especially a kind of cement method of denitration.

Background technology

" 12 " period, country will strengthen the emission control to nitrogen oxides." 12 " period China's nitrogen oxides Total emission volumn to reach to reduce discharging the target of 10%.This is accomplished by strengthening the nitrogen oxides producing the industries such as electric power, cement, metallurgy It is controlled.The discharge capacity of cement industry nitrogen oxides account for the whole nation industrial discharge total amount about 15%, be occupy thermal power generation, The third-largest discharged nitrous oxides rich and influential family after vehicle exhaust.No. 582 files of Ministry of Industry and Information are about the finger of cement industry energy-saving and emission-reduction Lead suggestion, it is proposed that concrete quantified goal: to " 12 " end, nitrogen oxides reduced by 25% on the basis of 2009.Simultaneously Pointing out, newly-built or reorganization and expansion cement (grog) production line project must configure denitrification apparatus.And denitration efficiency is not less than 60%.Cause This, the denitration technology inquiring into cement industry the most feasible seems the most urgent.

Rotary kiln is the key technology equipment that new type nonaqueous cement material burns till, and is also the main source of NOx.Calcining cement The approach generating nitric oxide NO during grog mainly has four kinds, i.e. the first heating power NOx, it is that fuel is cement kiln head 1400 DEG C More than can produce a large amount of NOx during burning；The second wink sends out NOx, it be have hydrocarbon in the presence of, send out formation in flame front wink NOx, the ratio that general this wink sends out NO growing amount is the least；The third fuel NO, it is by chemical bond nitrogen contained in fuel Produced.Because the joint of nitrogen-atoms can be less in fuel, so producing in the dore furnace of quality coal in cement kiln systems relatively low temperature Raw fuel NO_x is more；4th kind of raw material NOx, it is by the NOx formed after decomposing containing nitrogen compound in kiln feeding.? NO in kiln waste gas₂Normally only account for NO+NO₂Less than the 5% of total amount, NO then accounts for more than the 95% of total amount.The cement produced with the dry method of domestic operation Kiln NOx emission concentration is about 900～1700mg/Nm³Left and right.

In China, NOx conventional on new type nonaqueous cement rotary kiln controls technology mainly to be had following several: one is to optimize kiln Combustion system with dore furnace；Two is to change proportion scheme, mixes mineralizer in the hope of reduction sinter leaching temperature and time, improvement Grog burn-ability；Three is the burner using low NOx；Four is the stage burning technology in kiln tail dore furnace and pipeline.But, Even if above-mentioned four kinds of measures are all used, in fact the NOx emission of cement kiln also is difficult to reach 400mg/Nm³Below.

Summary of the invention

The present invention is directed to the deficiencies in the prior art, propose a kind of cement method of denitration, rationally distributed, easy and simple to handle, discharge NOx reach 400mg/Nm³Below.

In order to realize foregoing invention purpose, the present invention provides techniques below scheme: a kind of cement method of denitration, at selectivity After non-catalytic reduction denitration method completes, then through selective-catalytic-reduction denitrified method.

Further, described SNCR denitration method be spray in the middle and lower part of dore furnace or burner hearth carbamide or Ammonia.

Further, the pressure spraying into carbamide or ammonia is: the fluid pressure at nozzle is 0.4MPa, the gas at nozzle Pressure is 0.3MPa.

Further, described selective-catalytic-reduction denitrified method is for be provided with selectivity between kiln tail preheater and conditioning Tower Catalytic reduction reaction tower.

Compared with prior art, the invention have the advantages that catalyst amount is little, SCR reaction tower volume is little, and space is fitted Ying Xingqiang, denitrating system resistance is little, reduces SO₂To SO₃Conversion, reduce corrosion harmfulness, simplify reductant injection system.

Detailed description of the invention

Describing the present invention below in conjunction with detailed description of the invention, the description of this part is only exemplary and explains Property, protection scope of the present invention should there be is not any restriction effect.

Cement method of denitration, typically uses SNCR (SNCR) denitration method or SCR (SCR) denitration method, is the most individually carried out:

1 SNCR denitration technology

2.1 technological process

SNCR denitration technology is under conditions of not having catalyst, within the temperature range of 950～1050 DEG C, reducing agent (ammonia Gas or carbamide) spray in cement furnace, reducing agent is sent out with the nitrogen oxides (mainly nitric oxide and nitrogen dioxide) in stove Biochemical reaction, generates nitrogen and water, thus reduces the discharge of nitrogen oxides in effluent.

Reducing agent carbamide [CO (NH is sprayed in the middle and lower part of dore furnace or burner hearth₂)₂] or ammonia (NH₄OH), there iing part oxygen Under conditions of existence, there is following course of reaction.

4NH₃ + 4NO + O₂ →4N₂ + 6H₂O (1)

Temperature raises further, then it may happen that following reaction:

4NH₃ + 5O₂ →4NO + 6H₂O (2)

When temperature is less than 800 DEG C, NH₃The slowest with the response speed of NO；When temperature is higher than 1100 DEG C, reaction equation (2) can gradually Play a leading role, the NH when temperature is higher than 1300 DEG C₃The trend being changed into NO can become obvious.

1) carbamide supply station

When selecting carbamide as denitrification reducing agent, urea storage system, urea liquid compounding system and urea liquid store system System centralized arrangement, collectively constitutes carbamide supply station.Carbamide station capital equipment includes: dry carbamide warehouse, measuring chute, helical feed Machine, dosing pond, urea liquid storage tank, urea liquid delivery pump and water force (forcing) pump.In carbamide station, complete urea storage, carbamide The task of solution preparation, is pumped into stokehold spraying system.

2) stokehold spraying system

Stokehold spraying system is made up of N shell jetted layers, and every layer is made up of M ejector.It is suitable that N shell jetted layers is arranged in stove Position, to adapt to furnace flue gas variations in temperature, makes urea liquid spray in stove at optimal reaction temperature window.Every jetted layer Being designed with total valve and control whether this jetted layers puts into operation, the ejecting gun not put into operation then is exited stove thorax by pneumatic booster drive and keeps away Exempt from high-temperature heating.It is equipped with control valve on the urea pipeline of each jetted layers and atomizing steam pipeline, controls the stream of jetted layers Amount.

3) automatic control system

Automatic control system uses independent programmable logic controller (PLC), and system is separately provided 1 engineer station and (holds concurrently Operator station), reserved OPC communication interface communicates with DCS of Power Plant (DCS);System is provided with the form of necessity, looks into The functions such as inquiry and warning.Control system, according to the coherent signal gathered, controls, regulates capital equipment ruuning situation and spray gun fortune Market condition, realizes NO_x Reduction by Effective.

2.2 key technical problem

SNCR technology it is crucial that: reducing agent is injected in suitable temperature window, and the reducing agent sprayed into and NO in flue gas_X's It is sufficiently mixed, thus realizes higher denitration efficiency, reduce consumption and the escape amount of afterbody ammonia of reducing agent.

1) determination of nozzle location

Determine that nozzle location mainly considers the gas temperature within stove, carbamide reduction NO_xThe preference temperature of reaction is 950 DEG C～1050 DEG C.The position of nozzle chooses whether properly, directly to determine the height of the denitration efficiency of SNCR.The choosing of nozzle location Selecting is the place of whole SNCR system most critical.

Select suitable nozzle location, mainly realized by two kinds of approach:

CFD flow field simulation, determines optimal spray site；

It is distributed by infrared scene test furnace kiln temperature, determines eject position.

2) the atomization requirement of urea liquid

After urea liquid is injected to stove, it is desirable to carbamide and NOx must complete reaction in a short period of time, and otherwise carbamide is just Relatively low temperature province can be flow to, substantially reduce the extent of reaction of carbamide reduction NOx.In order to make the reaction of carbamide and NOx Complete in a short period of time, it is necessary to urea liquid is carried out good atomization.Urea liquid is carried out good atomization, must Liquid, gas pressure and flow at the structure of palpus selection nozzle and nozzle.Fluid pressure at nozzle is generally 0.4MPa, spray Gas pressure at mouth is generally 0.3MPa.

3) structure of nozzle and material

The quality of nozzle is the key problem in technology that carbamide adds equipment, and first the structure design of nozzle should ensure to make urea liquid have Having good atomizing effect, next is considered as nozzle itself and is in high temperature position, should have good heat resistance, is difficult to burn Damage.

The Railway Project that 2.3 cement furnace SNCR denitration technology should be noted that

1) current domestic typically no 50% ready-made urea liquid buying, joins voluntarily so packed carbamide need to be bought from chemical fertilizer factory Make urea liquid.Owing to the course of dissolution of carbamide is the endothermic reaction, need to configure powerful in urea liquid process for preparation Thermal source, in case carbamide dissolve after recrystallization.Under the meteorological condition of north cold area, it is brighter that this problem will expose Aobvious.

2) in whole SNCR denitration technique, urea liquid is always at heated state.If the dissolving water of carbamide and dilute Releasing the much higher hard of water (generally industry water), in heating process, the calcium in water, magnesium ion precipitation can cause denitrating system Incrustation of pipe, blocking.Therefore, it is necessary to add antisludging agent in carbamide or use demineralized water as denitrating technique water.

3) it is operated in stove internal high temperature district due to nozzle injector, for preventing ejector cooling water pipeline internal incrustation, Demineralized water need to be used to cool down water as multiple nozzle spraying device.

4) in SNCR denitration technique, the consumption of station-service gas is also bigger.Jet atomization, equipment cooling need, pipeline blow Sweep and be required for station-service gas.

2 SCR denitration technology

3.1SCR reduces NOx principle

SCR denitration technology be utilize reducing agent under catalyst action selectively with the nitrogen oxides in stove (mainly Nitric oxide and nitrogen dioxide) there is chemical reaction, generate nitrogen and water, thus reduce the one of nitrogen oxides in effluent discharge Denitrating technique.

Use SNCR denitration technology, it is ensured that the discharge of cement kiln NOx is stable at 800mg/Nm³, can be reliable Realize.But reach 400 mg/Nm³The most even lower, rely solely on SNCR and can not reliablely and stablely realize, it is necessary to and SCR denitration technology combines.The principle of SCR denitration technology is as follows:

4NO+4NH₃+O₂→4N₂+6H₂O

4NH₃+2NO₂+O₂→3N₂+6H₂O

NO₂+NO+2NH₃→2N₂+3H₂O

3.2 technological process

A SCR reaction tower is set up, by the waste gas of preheater by this reaction tower upper guide between kiln tail preheater and conditioning Tower Enter, mix mutually, by the catalytic action of multi-layer catalyst in reaction tower with reducing agents such as the ammonia sprayed in tower or carbamide, it is ensured that Denitrification reaction completes more fully, and catalyst is by V₂O₅、W₂O₃Isoreactivity component is made.

The key component of SCR denitration process unit includes a SCR reactor, a storage tank and a reducing agent note Enter system.Reducing agent anhydrous liquid ammonia the most with pressure, it is possible to be the ammonia spirit (usual weight concentration is 25%) under normal pressure. When using ammonia or urea liquid, generally it is directly injected into exhaust gases passes by being positioned at the atomizer of conduit or slip-stream In.The pressure store of anhydrous liquid ammonia depends on the temperature of storage tank.Liquefied ammonia is evaporated by steam, hot water or the electricity in vaporizer. Then, the ammonia of evaporation, through Dilution air, is injected in flue gas by injected system.Injected system has many injection nozzles Composition, makes ammonia and flue gas be uniformly distributed.On the other hand, in the case of nozzle quantity is less, can be in conjunction with a static mixing Device is used together.Ammonia being uniformly distributed for realizing NO in flue gas_XEffectively reduction, relatively low ammonia escaped quantity and thus Reach effectively utilizing of catalyst the most particularly significant.

Cost of investment in view of denitrating catalyst is higher, and cement furnace seldom relies solely on SCR and realizes aoxidizing nitrogen The control of thing.In the case of requiring relatively low concentration of emission, typically take the combined denitration skill that SCR with SNCR is combined Art.

The problem that 3.3 cement furnace SCR denitration techniques should be noted that

1) high dust concentration is big on the impact of catalyst

The dust content of cement furnace afterbody may be up to 80～100g/Nm³, easily cause catalyst pores blocking, make system pressure drop Increasing sharply, properly functioning to air-introduced machine causes serious threat, thus affects cement furnace production line and run steadily in the long term.

Cement furnace SCR denitration technique is to the blocking of catalyst and abrasion, it is proposed that higher requirement.

2) catalyst poisoning problem

The water-soluble alkali such as sodium, potassium compound V easily and in catalyst in cement furnace flue gas₂O₅Reaction causes in catalyst Poison, thus reduce the activity of catalyst.Meanwhile, the CaO content in cement furnace flue gas is higher, it is easy to SO₃Reaction generates CaSO₄, The surface of covering catalyst, reduces the activity of catalyst.

In cement furnace SCR denitration system, owing to flue gas neutral and alkali metal oxide content is higher, catalysis to be paid special attention to The poisoning problem of agent.

3 cement furnace SNCR+SCR combined denitration technology

The feature of 4.1 SNCR+SCR combined denitrations

1) catalyst amount is little

SCR technique is much more expensive due to catalyst so that the investment of SCR system is the biggest.And owing to needs regularly replace, run Expense is the highest.SNCR+SCR combined denitration technique is owing to initially with the preliminary denitration of SNCR technique, denitration efficiency can reach The highest to 40%, reduce the dependence to catalyst.Compared with SCR technique, the catalyst amount of hybrid technique can be significantly Reduce.

2) SCR reaction tower volume is little, and space adaptability is strong

Owing to combined denitration process catalyst consumption is few, arrange that SCR reacts by flue, extension flue etc. are carried out transformation Device, substantially reduces reactor upstream flue length.It is compared with single SCR technique, it is not necessary to complicated steel construction, saves Investment and the most limited by the field.

3) denitrating system resistance is little

Owing to the catalyst amount of combined denitration technique is few, SCR reactor volume is little, and its anterior flue is shorter therefore, with tradition SCR technique is compared, and system pressure drop will be greatly reduced, and decreases the workload of Induced Draft Fan, reduces operating cost.

4) SO is reduced₂To SO₃Conversion, reduce corrosion harmfulness

Although the use of catalyst is favorably improved denitration efficiency, but there is also enhancing SO₂To SO₃The side effect converted, and cigarette SO in gas₃The increase of content, will generate more NH₄HSO₄。NH₄HSO₄Cohesiveness very strong, when flue-gas temperature is relatively low, meeting Upstream device is also caused corrosion by blocking catalyst.Combined denitration technology, owing to decreasing the consumption of catalyst, will make this ask Topic obtains a certain degree of containment.

5) reductant injection system is simplified

In order to obtain NO_x Reduction by Effective reaction, it is desirable to the ammonia sprayed into and the NO in flue gas_XThere is good contact and require in catalysis anti- Flow field, concentration field and the temperature field being evenly distributed is formed, to this end, single SCR technique is except the ammonia that must be provided with complexity before answering device Outside injection grid (AIG) and control system thereof, also tend to need to lay in many places blending facility, lengthen flue with ensure AIG with The measures such as the most remote distance are had, to reach above-mentioned requirements between catalyst.And the reductant injection system of hybrid technique is arranged On boiler setting, with the SCR reactor in downstream apart from far, it is therefore not necessary to install mixing facility again additional, without lengthening cigarette Road, it is possible to obtain good reducing agent and NO at hydrogen-catalyst reactor entrance_XMixing and distribution.

4 brief summaries

1) from the point of view of world wide, the cement plant denitration engineering having been carried out, almost all uses SNCR denitration technology.SNCR denitration It it is the mainstream technology of current cement industry denitration.

2) efficiency of the denitration of SNCR method is 50%～60%, less than the efficiency of selective catalytic reduction (SCR) denitration (80%～90%), and the expense of SNCR method only has about 1/5th of SCR method.

3) SCR denitration technology can efficiently control the discharge of nitrogen oxides, it is ensured that the NO of furnace flue gas_XDischarge dense Degree drops to 100～200mg/Nm³.But SCR needs use and consume expensive noble metal catalyst, and due to cement production enterprise The dust concentration of waste gas is the highest, and alkali metal content is higher, easily makes catalyst poisoning and blocking.SCR denitration technology is in cement industry On practice the most just start, the space of the most many improvement.

4) along with the development of cement industry and improving constantly of environmental protection standard requirement, SNCR and SCR denitration will obtain extensively General utilization.

The above is only the preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art For Yuan, under the premise without departing from the principles of the invention, it is also possible to make some improvements and modifications, these improvements and modifications also should It is considered as protection scope of the present invention.

Claims

1. a cement method of denitration, it is characterised in that: after SNCR denitration method completes, then through selectivity Catalytic-reduction denitrified method.

2. cement method of denitration as claimed in claim 1, it is characterised in that: described SNCR denitration method is to divide The middle and lower part solving stove or burner hearth sprays into carbamide or ammonia.

3. cement method of denitration as claimed in claim 2, it is characterised in that: the pressure spraying into carbamide or ammonia is: at nozzle Fluid pressure is 0.4MPa, and the gas pressure at nozzle is 0.3MPa.

4. cement method of denitration as claimed in claim 1, it is characterised in that: described selective-catalytic-reduction denitrified method is at kiln tail Selective catalytic reduction reaction tower it is provided with between preheater and conditioning Tower.