CC BY
21
UDC 532.527
R. R. Usmanova, G. E. Zaikov
THE NEW EQUIPMENT FOR CLEARING OF TECHNOLOGICAL GASES
Keywords: Gas emission; Industrial zone; gas cleaning; scrubber; Technical and economic efficiency.
The guideline of the European parliament 96/61/ЕС on prevention of ecological pollution establishes the list of requirements for the industrial enterprises. The basic direction of their development is creation of drainless technological systems on the basis of the existing enterprises and perspective methods of clearing of gas. The new equipment which corresponds to industrial ecology requirements is developed. One of the major advantages of configuration of systems of a gas cleaning is possibility of the closed cycle of an irrigation thanks to system internal circulation of a liquid in the apparatus. Technical and economic indicators of new devices considerably exceed known analogues.
Ключевые слова: газовые выбросы; промышленная зона; газоочистка; газопромыватель; технико-экономическая
эффективность.
В руководстве Европейского парламента 96/61/ЕС по предотвращению экологического загрязнения устанавливается перечень требований для промышленных предприятий. Основным направлением развития является создание бессточных технологических систем на основе существующих предприятий и перспективных методов очистки газа. Разработано новое оборудование, отвечающее требованиям промышленной экологии. Основным преимуществом предложенной схемы газоочистки является возможность замкнутого цикла орошения благодаря системе внутренней циркуляции жидкости в аппарате. Технико-экономические показатели новых устройств значительно превышают известные аналоги.
1. The international control and the government quality of environment
The international cooperation in the field of wildlife management is carried out normally under the scheme: carrying out of the international meetings - the conclusion of contracts - creation of the international organisations -working out and coordination of programs of environmental safety.
Intensive development of economic activities of people, failures and accidents on industrial and defensive objects became destructive environmental impact and have led the nature to a condition of the crisis threatening by ecocatastrophe.
Therefore before mankind there was a harmonious exploitation problem in a combination to effective decrease in deleterious effect of industrial production on environing natural habitat.
Prompt formation of the increasing quantity of a waste is a subject of anxiety European Parliament. Guideline European Parliament 96/61/EC on the integrated pollution prevention and the control over them has been accepted on September, 24th, 1996 [1].
The guideline establishes the list of ecological requirements for the industrial enterprises, which enterprises should carry out to obtain the permit to the activity.
Member countries of the European parliament undertake to take necessary measures to guarantee that during work of the enterprise of a condition:
Undertake all necessary preventive actions on environmental pollution prevention, in particular, by application of the best existing technologies; do not make considerable environmental pollution; prevent formation of a scrap in conformity; with the guideline on a scrap.
Technologies without waste and landlocked cycles -one of the most radical measures of protection of environment from pollution. Four basic directions of their development (according to the Declaration on technology
without scrap and reclamation of scrap materials) [2] are more low formulated:
1. Creation of drainless technological systems of different function on the basis of existing and perspective methods of clearing and a reuse of the cleared runoffs.
2. Working out and introduction of systems of processing industrial and a human refuse which are considered thus as secondary material resources.
3. Working out of technological processes of reception of traditional kinds of production by essentially new methods at which the greatest possible carrying over of substance and energy on finished goods is reached.
4. Working out and creation of industrial complexes with landlocked structure of material streams and production residue in them.
The analysis of the data about a condition of an environing natural habitat of the Russian Federation shows that the total quantity of atmospheric emissions from industrial sources in 2014 has made about 32 million tons of harmful substances. The composition of gas emissions is resulted in table 1.
Table 1 - Results of posttest examination
Compound Concentration at the inlet, g/m3 Concentration after clearing, g/m3 Quantity of emissions, mill tons
Dust 0,02 0,00355 14,8
NO2 0,10 0,024 7,6
SO2 0,03 0,0005 9,2
СО 0,01 0,0019 3,5
On Figure 1 the scheme of rationing of admixtures in air taking into account their carrying over and dispersion to atmosphere [4] is introduced. Performance of condition CB < maximum concentration limit, where Cv -concentration of harmful substance will be a condition of environmental safety for the person, mg/m3. In a ground layer of atmosphere of human settlements maximum
concentration limit which values are resulted in «the Sanitary code of designing of industrial enterprises SN 3917-05» are established [3].
C>Max permissible concentration
Gas emission
C<MPC
Industrial zone
Zone of dispersion of admixtures
Residential area
J".................
Fig. 1 - Norms of admixtures of harmful substances in various zones
The total of the weighed particles arriving in atmosphere as a result of diverse human activity (according to experts European Parliament), becomes commensurable with quantity of pollution of a natural origin.
The dust in the gases departing from raw and cement dryers, mills, roasting furnaces, in air from transport devices, is a consequence of imperfection of the equipment and technological processes.
2. Clearing and processing of technological gases
Environment protection against pollution includes special methods and cleaning equipment of gas, waste regaining and secondary use of warmth and the maximum decrease in pollution. For this purpose develop technological processes and the equipment, meeting the requirements of industrial ecology.
To clearing of gaseous emissions for the purpose of their detoxication or extraction from them expensive and scarce ingredients apply the various clearing equipment and corresponding processing methods.
Now methods of clearing of dusty gases classify inheriting groups;
I. "Dry" mechanical dust extractors.
II. Filters.
III. Electric separators.
IV. "Wet" dust removal devices.
Mechanisms of dust collection. The basic operations in dust collection by any device are separation of the gasborne particles from the gas stream by deposition on a collecting surface; retention of the deposit on the surface; and removal of the deposit from the surface for recovery or disposal. The separation step requires application of a force that produces a differential motion of a particle relative to the gas and a gas retention time sufficient for the particle to migrate to the collecting surface. The principal mechanisms of aerosol deposition that are applied in dust collectors are gravitational deposition, flow-line interception, inertial deposition, diffusional deposition, and electrostatic deposition.
Thermal deposition is only a minor factor in practical dust-collection equipment because the thermo force is small. Two other deposition mechanisms, in addition to the six listed, may be in operation under particular circumstances. Some dust particles may be collected on filters by sieving when the pore diameter is less than the particle diameter. Except in small membrane filters, the sieving mechanism is probably limited to surface-type filters, in which a layer of collected oust is itself the principal filter medium.
The other mechanism appears in scrubbers. When water vapor diffuses from a gas stream to a cold surface and condenses, there is a net hydrodynamic flow of the gas directed toward the surface. This flow, termed the Stefan flow, carries aerosol particles to the condensing surface and can substantially improve the performance of a scrubber. However, there is a corresponding Stefan flow directed away from a surface at which water is evaporating, and this will tend to repel aerosol particles from the surface.
In addition to the deposition mechanisms themselves, methods for preliminary conditioning of aerosols may be used to increase the effectiveness of the deposition mechanisms subsequently applied. One such conditioning method consists of imposing on the gas high-intensity acoustic vibrations to cause collisions and flocculation of the aerosol particles, producing large particles that can be separated by simple inertial devices such as cyclones. This process, termed "sonic agglomeration," has attained only limited commercial acceptance.
Another conditioning method, adaptable to scrubber systems, consists of inducing condensation of water vapor on the aerosol particles as nuclei, increasing the size of the particles and making them more susceptible to collection by inertial deposition.
Most forms of dust-collection equipment use more than one of the collection mechanisms, and in some instances the controlling mechanism may change when the collector is operated over a wide range of conditions. Consequently, collectors are most conveniently classified by type rather than according to the underlying mechanisms that may be operating [4].
Dust-collector design. In dust-collection equipment, most or all of the collection mechanisms may be operating simultaneously, their relative importance being determined by the particle and gas characteristics, the geometry of the equipment, and the fluid-flow pattern. Although the general case is exceedingly complex, it is usually possible in specific instances to determine which mechanism or mechanisms may be controlling. Nevertheless, the difficult of theoretical treatment of dust-collection phenomena has made necessary simplifying assumptions, with the introduction of corresponding uncertainties. Theoretical studies have been hampered by a lack of adequate experimental techniques for verification of predictions. Although theoretical treatment of collector performance, been greatly expanded in the period since 1980, few of the resulting performance models have received adequate experimental confirmation because of experimental limitations.
The best-established models of collector performance are those for fibrous filters and fixed-bed granular filters, in which the structures and fluid-flow patterns are
reasonably well defined. These devices are also adapted to small-scale testing under controlled laboratory conditions. Realistic modeling of full-scale electrostatic precipitators and scrubbers is incomparably more difficult. Confirmation of the models has been further limited by a lack of monodisperse aerosols that can be generated on a scale suitable for testing equipment of substantial sizes. When a polydisperse test dust is used, the particle-size distributions of the dust both entering and leaving a collector must be determined with extreme precision to avoid serious errors in the determination of the collection efficiency for a given particle size.
The design of industrial-scale collectors still rests essentially on empirical methods, although it is increasingly guided by concepts derived from theory. Existing theoretical models frequently embody constants that must be evaluated by experiment and that may actually compensate for deficiencies in the models.
Mechanical centrifugal separators. A number of collectors in which the centrifugal field is supplied by a rotating member are commercially available. In the typical unit shown in Figure 2, the fan and dust collector are combined as a single unit. The blades are especially shaped to direct the separated dust into an annular slot leading to the collection hopper while the cleaned gas continues to the scroll.
As a result of scrubber laboratory researches operating modes at which its efficiency many times over exceeds efficiency of analogous apparatuses are installed.
j?
Fig. 2 - Scheme of the experimental equipment (Patent RF №2339435) [5]: 1 - scrubber; 2 - the actuator; 3 - bunker dust; 4 - the electric motor; 5 -screw feeder; 6 - fan; 7 - the diaphragm; 8,10 -differential pressure gauges; 9 - the samplers; 11 -the aspirator; 12 - pressure tank; 13 - flow meters; 14 - the samplers
Although no comparative data are available, the collection efficiency of units of this type is probably comparable with that of the single-unit high-pressure-drop-cyclone installation. The clearances are smaller and the centrifugal fields higher than in a cyclone, but these advantages are probably compensated for by the shorter gas path and the greater degree of turbulence with its inherent reentrainment tendency. The chief advantage of these units lies in their compactness, which may be a prime consideration for large installations or plants requiring a large number of individual collectors. Caution
should be exercised when attempting to apply this type of unit to a dust that shows a marked tendency to build up on solid surfaces, because of the high maintenance costs that may be encountered from plugging and rotor unbalancing.
They have been used to collect chemical incinerator fume and mist as well as sulfuric and phosphoric acid mists. The collection efficiency of a scrubber is highly dependent on the throat velocity or pressure drop, the liquid-to-gas ratio, and the chemical nature of the particulate. Throat velocities may range from 60 to 150 m/s (200 to 500 ft/s). Liquid injection rates are typically 0,59 to 1,5 m3/1000 m3 of gas. A liquid rate of 1,1 m3/1000 m3 of gas is usually close to optimum, but liquid rates as high as 3,2 m3 have been used. Efficiency improves with increased liquid rate but only at the expense of higher pressure drop and energy consumption. Pressure-drop predictions for a given efficiency are hazardous without determining the nature of the particu-late and the liquid-to-gas ratio. In general, particles coarser than 1 microns can be collected efficiently with pressure drops of 20 to 65 cm of water. For appreciable collection of particles, pressure drops from 65 to 120 cm of water are usually required. When particles are appreciably finer than 0,7 microns, pressure drops of 180 to 280 cm of have been used.
to 400
0 300
1 200
jË 1i CD
£ Л-c5 60
~ 50 7:1 <«0 a.
О 30
20
Terminal velocity Zero relative velocity
3 4 SÍ78SÍ
.......
3 4 5 6 789т
2 3 4 S S 7 89%
Time for complete evaporation, sec Fig. 3 - Effect of drop diameter on time for complete evaporation of water drops
Figure 3 is easy to use to estimate the necessary spray dispersion. For typical conditions of 300°F gas inlet temperature and a 20°F approach to adiabatic saturation at the outlet, a 60 microns droplet will require about 0,9 s to evaporate, while a 110 microns droplet will require about 3 s. If the time available for drying is no more than 3 s, it therefore follows that the largest droplets in a humidifier spray should be no larger than 100 microns. If the material being dried contains solids, droplet top size will need to be smaller due to slower evaporation rates. Droplets this small not only require considerable expensive power to generate, but since they have inherent penetration distances, they require expensive dispersion arrangements to get good mixing into large gas flow's without allowing damp, stick particles to reach walls.
3. Self-induced spray scrubbers
Self-Induced Spray Scrubbers form a category of gas-atomized spray scrubbers in which a tube or a duct of some other shape forms the gas-liquid-contacting zone.
The gas stream flowing at high velocity through the contactor atomizes the liquid in essentially the same manner in a rotoklon. However, the liquid is fed into the contactor and later recirculated from the entrainment separator section by gravity instead of being circulated by a pump as in rotoklon.
Rotoklon represents the basin with water on which surface on a connecting pipe dusty gas arrives. Over a water surface gas is developed, and a dust containing in gas by inertia penetrate into a liquid. Turn of shovels impeller is made manually, rather each other on a threaded connection. The slope of shovels was installed in the range from 25 ° to 45 ° to an axis. In rotoklon three pairs blades sinusoidal a profile, the adjustments of their position executed with possibility are installed. Depending on a dustiness of a gas stream the bottom blades by means of flywheels are installed on an angle matching to an operating mode of the device.
The scheme is well illustrated in Figure 4.
100
Fig. 4 - Scheme of the experimental equipment (Patent RF №2317845) [6]: 1 - rotoklon; 2 - batcher; 3 - qualifier; 4 - collector of a coarse dust; 5 -cyclone; 6,7 - gas pipeline; 8 - fan; 9 - potentiometer; 10 - differential pressure gauge; 11 - diaphragm
Although self-induced spray scrubbers can be built as high-energy units and sometimes are, most such devices are designed for only low-energy service. The principal advantage of self-induced spray scrubbers is the elimination of a pump for recirculation of the scrubbing liquid. However, the designs for high-energy service are somewhat more complex and less flexible than those for venturi scrubbers.
One of the problems in predicting efficiency and required pressure drop of a rotoclon is the chemical nature or wettability of the particulate, which on 0,6 microns size particles can make up to a threefold difference in required pressure drop for its efficient collection. Nonatomizing froth scrubbing is described in tliose patents as occuring within defining boundaries on a new dimensionless velocity versus dimensionless liquid/gas ratio two-phase flow regime map, shown here as Figure 5.
10
о
UWCOALESCED
NONFLOODED
001
01
10
100
Fig. 5 - Spray scrubbing flow regime map
As a result of researches dependence of water resistance dynamic scrubber on speed turbulent flow has been installed. Apparently from Figure 6 with growth of speed turbulent flow to 27 mps separation efficiency raises to 78 %. The subsequent increase in speed over the range from 30 mps to 40 mps is accompanied by reduction of efficiency of separation to 63 %.
Calvert reports pressure drop through tube banks to be largely unaffected by liquid loading and indicates that s correlations for gas flow normal to tube banks or data for gas flow through heat-exchanger bundles can be used. However, the following equation is suggested:
AP=8,5-10-3qpU2 (1)
where AP is cm of water; n is the number of tubes; p is the gas density, g/cm3; and U is the actual gas velocity between tubes, cm/s. Calvert did find an increase in pressure drop of about 80 to 85 percent above that predicted by Equation in vertical upflow of gas through tube banks due to liquid holdup at gas velocities above 40 mps.
tb%
8Ü
50
20
Л /
/
<лР
лР,kPa
1,5
1,0
0,5
10
20
30
40 u,mps
Fig. 6 - Dependence of efficiency of a gas cleaning n and pressure losses (AP) on entrance speed of a gas stream
Simultaneously with increase in speed of a gas stream the water resistance of the apparatus from 578 to 1425 Pascal raises also. Optimum result it is possible to see of 25 mps, in this case efficiency of clearing at speed makes 78 %, at head losses no more than 1200 Pascal. By fractional efficiency n sizes of dispersion particles which are most effectively trapped by the apparatus have been defined.
General efficiency of a gas cleaning count by formula:
^ = 1 - exp
vnWQ
57,3Ub tan 0
(2)
where n is the fractional primary collection efficiency; u is the drop terminal centrifugal velocity in the normal direction, mps; U is the superficial gas velocity, m/s; n is the number of rows of baffles or bends; 0 is the angle of inclination of the baffle to the flow path,°; W is the width of the baffle, m; and b is the spacing between baffles in the same row, m.
For drop terminal centrifugal velocity of: u = d2pa/18^
where d and p are the drop particle diameter, cm, and particle density, g/cm3, respectively; ^ is the gas viscosity, P; and a is the acceleration due to centrifugal force. It is defined by the equation:
a = 2U2 sin 0/W cos3 0
Efficiency of trapping of corpuscles in rotoklon depends as on characteristics of trapped corpuscles (a size and density), and from operating conditions among which the most important is speed of a gas stream at passage of shovels impeller, thus, the formula (2) opens physical sense of the processes proceeding in contact channels rotoklon.
One of the major advantages of configuration of systems of a gas cleaning "Rotoklon" is possibility of the closed cycle of an irrigation thanks to system internal circulation of a liquid in the apparatus.
4. Feasibility report of a choice of system of clearing of gas
Enormous scales of industrial activity of the person promoted a sharp decline of a state of environment that can cause far-reaching negative aftereffects for mankind. Last years the legislative deeds sharply raising the demands to protection of a free air [3] are published. The industrial factories are aimed to that the equipment for gas clearing was highly effective, reliable and inexpensive, that is would have high technical-and-economic indexes.
Designing of apparatuses for gas clearing in Russia in total loses world level. Work on elimination of this problem is made by slow rates. Protection of an aerosphere against pollution represents the important problem and its scientific implementation is still far from perfect.
The main task is decrease in volumes of the flying emissions during the basic process. Quite often economic benefit gained in sphere of the basic manufacture, is completely recoated by expenses for clearing of great volumes of gas emissions. The role of treatment facilities in system of provisions on aerosphere protection consists in liquidation of those emissions which cannot be prevented preventive measures.
The following was the primary goals which were put by working out of new apparatuses for gas clearing:
• to develop criteria the feasibility report of efficiency of clearing systems;
• to create apparatuses for clearing of gas emissions of the basic industrial systems of a fine dust with a wide range of change of technological parametres.
The Technical and economic estimation of installations for gas clearing is based on the comparative
data. The installation of a gas cleaning is compared on technical and economic parametres with the best functioning analogous installation. The analogue is led to the conditions comparable to conditions of sized up installation (power, separation efficiency, conditions of production). Comparison is made on capital investments, productivity, operational expenses.
The method of calculation of relative efficiency the installations has been developed, allowing to find the most rational constructive solutions for system of trapping of gas emissions. Generally, the damage from gas emissions can be defined as Y=B-M.
If to express ecological efficiency of the developed design from the point of view of the least damage put to an aerosphere the ecological damage in this case will register in the form of Ym — min. Value Ym decreases with magnitude growth: N
m¡ • c0¡
Е =■
i=1
N
(3)
b • xA -(1 -n)-C
¡=1
It is possible to consider magnitude E as criterion the technician of a economic estimation of installations for gas clearing. The criterion of ecological efficiency e will register as a relationship of values E computed for new installation E1 and base analog of E0: e = E1 / E0.
Thus, for two installations of a gas cleaning of the concrete manufacture, discriminated in the separation extent, ni ^n0, the ecological system effectiveness is defined the technician in ecological parametre e ^ max.
The prevented ecological damage Yp is computed as a difference: Yp= Y0 - Yh between economic losses of competing systems.
The gained results have illustrative character and show possibility of application of criterion of feasibility report e for the comparative analysis of apparatuses for gas clearing. Comparison of the developed gas apparatuses with other apparatuses applied now, on technical-and-economic indexes shows the big advantages of the first. New apparatuses are simple, low-cost and effective gas apparatuses. At the best separation efficiency of gas from a dust their sizes, weight and cost it is less, than at the majority of other devices for gas clearing.
Conclusions
1. The solution of an actual problem on perfection of complex system of clearing of gas emissions and working out of measures on decrease in a dustiness of air medium of the industrial factories for the purpose of betterment of hygienic and sanitary conditions of work and decrease in negative affecting of dust emissions given.
2. Designs on modernization of system of an aspiration of smoke gases of a flare with use of the new scrubber which novelty is confirmed with the patent for the invention are devised. Efficiency of clearing of gas emissions is raised. Power inputs of spent processes of clearing of gas emissions at the expense of modernization of a flowchart of installation of clearing of gas emissions are lowered.
3. Ecological systems and the result of the implementation of the recommendations is to a high degree of purification of exhaust gases and improve the ecological situation in the area of production. The economic effect of the introduction of up to 3 million rubles/ year.
References
1. Directive 2000/76/EC of the European Parliament and of the Council of 24 December 1996 on the incineration of waste
2. Decision 1600/2002/EC of the European Parliament and of the Council of 22 July 2002 laying down the Sixth Community Environment Action Programme.
3. GOST 17.2.3.02-05. Wildlife management. Atmosphere, 2005.
4. Mel Pell, James B. Dunson, Ted M. Knowlton. Gas-Solid Operations and Equipment. Handbook. USA, 2008.
5. Patent №2339435 (2008).
6. Patent №2317845 (2008).
© R. R. Usmanova - She is currently Associate Professor of the Chair of Strength of Materials at the Ufa State Technical University of Aviation in Ufa, Bashkortostan, Russia, [email protected]; G. E. Zaikov - DSc. Professor of the Chair Plastics Technology Kazan National Research Technological University in Kazan, Tatarstan, Russia, [email protected].
© Р. Р. Усманова - канд. техн. наук, доц. каф. СМ Уфимского госуд. авиационного технич. ун-та, [email protected]; Г. Е. Заиков - д-р хим. наук, проф. каф. ТПМ КНИТУ, [email protected].
