European-type mill technology in environmental desulfurization of limestone milling

Introduction
SO2 emissions in the world, thermal power plants, coal-fired boiler SO2 pollution is most concentrated, the largest industry, but also the control of SO2 pollution in key industries. If these industry emissions of air pollutants is not effectively controlled, it will directly affect the sustainable development of China's economy and improve the environmental quality of the atmosphere. State always attached importance to environmental desulfurization work, especially to increase the thermal power plants, steel desulfurization supervision, requiring new construction, renovation and expansion of coal-fired power plants, metallurgical mills must meet the requirements for sulfur dioxide control targets.
Limestone - gypsum wet flue gas desulfurization processes (FGD) and boiler calcium spray process, is the world's most mature technology, the most widely used technology to control SO2 emissions, more than 90% of domestic thermal power plants using limestone - gypsum desulfurization.
Limestone - gypsum Desulfurization works: limestone powder made by adding water as the absorbent slurry is pumped into the absorber full contact with the flue gas mixed with the flue gas sulfur dioxide and calcium carbonate slurry from the lower portion of the column of air into the drum oxidation reaction of calcium sulfate, calcium sulfate after a certain saturation, gypsum crystals form. After exiting the absorber gypsum slurry was concentrated, dehydrated to a moisture content less than 10%, and then to the gypsum silo conveyor stack, flue gas desulfurization after removing the defogger through droplets, and then through a heat exchanger heating after warming up, the chimney into the atmosphere. Since the absorbent slurry within the absorption tower circulating pump through repeated cycles in contact with the flue gas, high efficiency absorbers, calcium sulfur relatively low desulfurization efficiency can be greater than 95%.
Boiler technology to spray calcium limestone as absorbent, limestone powder is injected into the furnace by the air force, in the furnace for the thermal decomposition of calcium oxide and carbon dioxide, calcium oxide and sulfur dioxide in the flue gas to produce calcium sulfite. Since the reaction between the gas-solid, and the reaction is slow, absorbent utilization is low. Therefore provided in the rear tail flue activation reactor humidifier, humidifying water was sprayed into the activation reactor, and unreacted calcium oxide in contact shall generate calcium hydroxide and then reacted with sulfur dioxide in the flue gas.
Whether calcium sprays boiler, or limestone - gypsum flue gas desulfurization purification after combustion, SO2 absorption media are limestone, limestone powder particle size have a greater impact on the desulfurization efficiency, the smaller the particle size, the more beneficial of SO2 absorption, limestone powder preparation has become the thermal power plants, steel desulfurization, improve desulfurization efficiency prerequisites. In addition, the production cost of limestone has a greater impact on the desulfurization costs. Low-cost production of high fineness limestone powder technology has become an important part of environmental desulfurization technology.

Several major factors that influence the efficiency of Limestone
1, limestone quality
Typically, the weight percentage of calcium carbonate in limestone should be higher than 85%, will be due to the impurities content is too low to run bring some problems, resulting in increased consumption and transportation costs absorbent, gypsum purity decreases.
Determined by the quality of the limestone content of CaO of limestone higher purity, better desulfurization efficiency. As the process design during the mix design, it is necessary to calculate the chemical composition, but also to understand its physical properties. A limestone calcium oxide content of the product was 48% - 54%; CaO content of the limestone does not necessarily require the higher the better. CaO> 54% limestone, and marble of high purity, easy grinding, chemical stability strong, not suitable for use as a desulfurization agent.
2, the particle size of limestone (fineness)
The fineness of limestone powder is an important factor in the efficiency of desulfurization, the contact area of the reaction largely determines the chemical reaction rate, the finer particles of limestone powder, the greater the mass specific surface area, the contact area per unit mass of the chemical reaction also greater. Since the dissolving limestone reaction is a solid - liquid two-phase reaction, the reaction rate is proportional to the specific surface area of the limestone particles, therefore, good resorption properties of fine limestone particles, a variety of related higher reaction rate can be faster HSO3- slurry reacts with the SO2 gas faster absorption, higher desulfurization efficiency and limestone utilization.
But limestone particle size is smaller, the higher the energy consumption broken. To grind finer limestone powder, the need for a larger mill, high energy consumption, increase investment, which requires trade-offs, considering. Usually it requires limestone powder through 250 mesh or 325 mesh sieve rate of 90%.
While limestone and limestone particle size quality related. To ensure the removal efficiency and limestone utilization reaches a certain level, when the high impurity content in limestone, limestone grinding should be finer number.
3, affect the reactivity of limestone desulfurization system performance
Limestone as the absorbent properties include not only its chemical composition, which mainly includes alkali reactive desulfurization system is provided by dissolution of limestone powder, the activity of the absorbent in the absorber solubility and dissolution rate, is a species transforming characteristics in an acidic environment. Absorber absorbers contain active species, physico-chemical properties and react acidic environment. Physico-chemical properties of the absorbent comprising: purity, crystal structure, impurity content, particle size distribution, comprising an inner surface (i.e., porosity), including the total surface area and particle density units. Higher activity while maintaining the same limestone limestone utilization, can reach a higher SO2 removal efficiency. High reactivity of limestone, limestone utilization is also high and low gypsum excess CaC03 content, namely high purity gypsum.
Limestone powder preparation and process technology
Desulfurization with limestone powder desired particle size of 250 mesh or 325 mesh (45μm), 325 mesh limestone powder and better desulfurization effect. Preparation of such a fine limestone powder, basically mill mainly Raymond (tilting mill), suspended roller mill, a ball mill or the European version of the mill several programs. In the past, Raymond, suspended roller mill, a ball mill to use more recent years, with limestone powder fineness requirements and the need to improve energy saving, more and more preparation plant desulfurization limestone powder began to use the European version mill program.
European-type mill system uses equipment: crushers, hoist, electromagnetic vibrating feeder, the European version of the mill. Since the separator means European version of the mill with internal without external separator, making the process simple.
Process outlined as follows: a large block of limestone by jaw crusher to the required particle size, the hoist will be sent to storage hopper, and then by the vibrating feeder evenly into the European version of quantitative continuous mill indoor machine host mill grinding, grinding after windblown limestone powder, the separator classification. In line with the fineness limestone powder with the air through pipes into the new isolation cyclone powder collector, separated collection. Finished limestone powder collected through the discharge port by the delivery device into the powder cartridge to prepare for the use of desulfurization. Substandard particles are separated by separator after being thrown to the cylinder wall, after falling back to the grinding mill along the cylinder wall. The entire system runs under negative pressure system to ensure dust does not spill site clean.
Since entering the limestone within the mill sometimes have a certain moisture content, the heat generated during polishing will make it into steam, so that the total increase in the gas system. And because the pipe joints with limestone or air into the system, will also increase the total amount of gas in the system. Grinding friction heat also cause the gas to heat up, the volume expansion. At this time in order to maintain a negative pressure operating state of the system can open the valve between the fan and the host so that excess gas automatically imported pulse bag filter after filtration is discharged to ensure environmental protection.
the European version of the mill structure and working principle
The whole structure of European-type mill consist the main unit, separator, pipeline equipment, centrifugal fan, isolated cyclone powder collector, dust composition.
Main unit works: motor driven transverse shaft through V-belt, the transverse drive shaft and then through the other end of the spindle drive bevel gear. The upper end of the spindle is connected to the hanger roller, roller shaft member through the cross arm hanging on the hanger roller, roller entire cross arm member is rotatable about the axis wobble. When the spindle is rotated, the roller member at the same time around the central axis of rotation, the centrifugal force of the roller rolling along the inner circle grinding ring. Roller blade knife hanger with the bottom, blade knife blade mounted under the seat pan fitted with the blade on the blade holder disc. The shovel blade material within the mill after scooping sent between RCC grinding ring and roller.
Separator work process: frequency conversion motor driven leaf discs, the rotation vane airflow formed on the disc, a large centrifugal force larger particulate material left behind after the tube wall to fall back to the mill, qualified materials through the separator . Motor speed according to finished powder particle size is adjusted accordingly: To obtain a more fine-grained powder neutrons, it should improve the speed of the blade, if you want to get coarser particle size powder midnight, it should reduce the rotational speed of the blades specific speed should be carefully adjusted according to the number of finished projects, the proportion of the material, the local temperature and humidity, barometric pressure and the level of the specific characteristics of the particles, mill use.
Cyclone powder collector performance mill plays a very important role. When pinkish airflow into the powder collector formed whirling airflow downward movement in the powder collector. Rotating particle under the influence of centrifugal force, the particles thrown to the cylinder wall. Once the particles encounter the cylinder wall that is captured and slide along the bottom of the barrel cylinder wall. Downward movement of the gas under the action of the rotating cone and is accelerated upward reflecting back from the discharge pipe into the fan. The lower end of the set is equipped with powder discharge valve, the powder will take away from the powder collector falling through the upper and lower cone valve. Due to the rotation of the core airflow upward powder collector conical bottom formed by a negative pressure state, so the lower end of the powder seal set demanding, does not allow leakage phenomenon. Once the leak would have been trapped in the powder will be blown away the gas re-direct impact on the whole production. Therefore, the lower end of the set is equipped with powder on the lower poppet valve, its role is opened or closed, respectively, so as to ensure that no outside air is drawn into the powder collector at the time of discharge.
the European version of the mill were prepared limestone powder technology
MTW European version of the mill is our latest European experts absorb grinding technology and philosophy, with great concentration to develop the latest grinding equipment with international advanced level of technology, with a number of independent patent technology, the model uses a bevel gear overall drive, internal lubrication system, curved duct latest patents (Patent No: ZL 2009 2 0088889.8, ZL 2009 2 0092361.8, ZL 2009 2 0089947.9). Stable performance, easy operation, low energy consumption; controllable adjustable product size, grinding materials widely applied; equipped with special dust, dust emission concentration is well below the national environmental regulations, has been in Guodian, Huadian, Huaneng, Datang, etc. It is widely used than under the limestone milling plant desulfurization project.
The main technical advantages are as follows:
1, the overall drive bevel gear, power loss, high efficiency: the traditional pendulum mill, suspended roller mill for an additional gear, by coupling the drive shaft, the installation of the difficulty, easy to produce noise, reduce efficiency, MTW European version of the mill for the overall drive bevel gear, more compact, more convenient installation adjustment, efficiency is greatly increased.
2, the internal lubrication system, advanced and reliable: the traditional mill in the form of lubricating grease lubrication, resistance, temperature rise, short bearing life, MTW European version of the mill with internal oil pump, without an additional oil pump or lubrication station, It can be achieved spindle bearings and bevel gear shaft bearing lubrication, which greatly improved the life of the equipment.
3, curved duct, the small amount of wind damage, the material flow is good: the traditional mill in Mill duct are bar-type duct. This structure exists duct board air impact generated resistance, large molecules collide with each other between the air flow energy loss, easy to produce eddy currents duct blockage and other shortcomings, MTW European version of the mill employed a curved duct-type air duct, cut imports to smooth airflow, resistance, internal export orientation is conducive to spread the material, blocking material is not easy.
4, special grinding roller and grinding ring structure design, curved blade interchangeable blade, so that the grinding efficiency, reduce costs: the traditional mill blade edge wear faster, the overall blade blade, blade portion after wear, We need to replace the whole blade, material waste, increasing down replacement. MTW European version of the mill blade, the blade made of high wear-resistant alloy materials, long life, simply replace the replacement blade part, improve material utilization. Further conventional planar blade, after scooping up the material deposited on one level, so that the central roller grinding ring wear serious, surface type blade material can be oriented facade, so that the ring roller mill, middle and lower part of the can grinding to uniform wear, but also increases the effective working area, thereby increasing the yield.
5, product size adjustable controllable, high efficiency separator: separator speed variable frequency control, more precise speed, better fines separation; isolated cyclone powder, the powder efficiency is greatly improved, and the inner cylinder the use of isolation structure between powder mixed gas stream, can effectively improve the efficiency of the separator and classifier accuracy.
6, without resistance into the wind volute (small observation door without vortex): a traditional mill into the wind volute observe the door sector board protruding outward facing, with air intake volute surface is not a plane, so it is easy to produce vortex effect, increasing energy consumption. MTW European version of the mill with internal door and the inner surface of the inner surface of the inlet volute on the same surface, so that we can effectively prevent the vortex effect.
7, user-friendly design, easy to operate: the European version of the mill not only uses a lot of advanced internal structure, but also used the appearance of a beautiful arc structure design, so that the whole machine more user-friendly, reducing the generation of workers to operate when necessary damage.
8, pay attention to environmental protection philosophy: Device operating noise, equipped with advanced dust, dust emission concentration is well below the national environmental regulations. Airflow created by the whirlwind powder collector upper return duct suction centrifugal fan, native entire airflow system is closed loop, and is in a state of negative pressure circulating, unique air circulatory system can greatly reduce the efflux air flow, reduce dust, environmentally friendly.
VI. European version of the mill selection in environmental desulfurization limestone powder preparation system
Environmental desulfurization limestone powder preparation system can run on 300 days uptime 20 hours a day, when calculating the amount of limestone powder single station according to required environmental desulfurization year yield, and then select from the time the European version of the mill stand-alone production the models and specifications. European version of the mill performance specifications for the preparation of limestone powder shown in Table 1.

	MTW110	MTW138	MTW175
Grinding ring inner diameter (mm)	Ф1100	Ф1380	Ф1750
Host speed (r/min)	120	96	75
Maximum feed size(mm)	< 30	< 35	< 40
Finished Size(mm)	1.6～0.045 The finest up to 0.038	1.6～0.045 The finest up to 0.038	1.6～0.045 The finest up to 0.038
Capacity(t/h)	3～10	6～20	10～35
Dimensions（mm）	8910×6950×9010	9860×8340×10227	13500×11500×9500

CONCLUSIONS
To sum up, the European version of the powder mill mechanism technology environmental desulfurization limestone powder preparation techniques, fineness and particle size distribution of their products are homogeneous, well over the required flue gas desulfurization limestone powder suitable to improve desulfurization effectiveness. Its production process smooth lines, investment start fast, easy production management. In the choice of the production process and equipment selection scheme, mature, reliable new technology, new technologies, so technologically advanced, economical, practical and reliable. Electrical automation control level to achieve reliable and practical. Attaches great importance to the comprehensive management of the environment, it can reach the national standard. Comprehensive energy consumption than traditional Raymond, suspended roller mill, a ball mill and other technology to reduce 20-30%, a substantial increase in product quality.
So the production line process since the advent of more and more favored by environmental desulfurization project, the European version of the mill in environmental desulfurization projects in a wide range of applications, will further promote the progress of environmental desulfurization work of thermal power plants, steel mills energy abatement technology and equipment to provide a reliable guarantee.