Optimization and operation practice of two sintering flue gas desulfurization process in Baosteel

2016-04-29 14:13:20

Abstract: This paper briefly introduces the technological principle and system of limestone gypsum flue gas desulfurization technology. The technique the since 2008 in Baoshan Iron and steel sintering has been put into use, in the subsequent operation process have CWMS, cooler, absorption tower, slurry supply and discharge device was improved and optimized for the operating system. The improvement measures have achieved remarkable results, and further promote the sintering process of emission reduction.
Key words: Limestone - gypsum method; desulfurization; sintering and emission reduction
1 Preface
During 11th Five-Year, although the iron and steel industry, energy saving and emission reduction achieved great success, but the sintering flue gas desulfurization technology is still staying in the thermal power and other desulfurization process of imitation, copying phase, has not made substantial progress. At present, the main problems of sintering flue gas desulfurization technology are not mature, the high price of desulfurization equipment, the two use of desulfurization byproducts, etc.. Baosteel rely on their own R & D system, based on iron and steel industry itself, with the successively in Baosteel Mei steel companies, Baosteel stainless steel company and Baosteel headquarters and large sintering machine on the successful operation of sintering flue gas characteristics of R & D with independent intellectual property rights of Baosteel sintering flue gas desulphurization technology -- swirl red tower of wet limestone - gypsum method], and achieved good results.
2 limestone - gypsum wet desulfurization technology
2.1 principles of Technology
After the sintering flue gas enters the absorption tower flue gas distributor through the two stages of the process water and the slurry, the flue gas is distributed through the aeration pipe to spray into the absorption tower slurry pool, and a stable bubbling layer is formed at the liquid level of the slurry pool. In the bubbling layer, gas phase is highly dispersed into the liquid phase, large gas-liquid contact area and high heat and mass transfer efficiency in the flue gas SO2 and slurry reaction created good thermodynamic and dynamic conditions and flue gas in the liquid bubble have similar water film dust removal effect, especially to 1 m below the dust effect is more obvious. Net smoke is after two level mist eliminator to remove the bulk of droplets by desulphurization chimney emissions. The process flow chart is shown in figure 1.
Desulfurization process is mainly in the absorption tower slurry tank, the main chemical reactions occur:
2.2 process system
Limestone - gypsum desulfurization process mainly by the flue gas system, SO2 absorption system, limestone slurry preparation system, gypsum dewatering system, wastewater discharge system and evacuation system subsystems composition.
Gas system: mainly is composed of a flue, booster fan, inlet baffle, outlet damper, bypass flue baffle, standby discharge facilities (standby chimney, standby discharge flue baffle) etc., flue gas system pressure and desulfurization device and flue gas bypass switch.
SO2 absorption system: mainly by the absorption tower, cooler, mist, oxidation fan, mixer and other components, to complete the cooling of flue gas, desulfurization, dust, and the formation of gypsum crystal.
Limestone slurry preparation system: mainly by the feeding facilities, wet ball mill, limestone cyclone station, limestone slurry transport facilities, complete the preparation and delivery of SO2 absorbent.
Gypsum dewatering system: mainly by the gypsum cyclone and vacuum belt dewatering machine, vacuum pump and other components, after dehydration treatment of gypsum surface water rate is not more than 10%, into the gypsum silo storage to be transported.
Wastewater discharge system: mainly by the waste water cyclone, waste water efflux pump. The form of wastewater discharged by Sinotrans, regular tankers Sinotrans disposal.
Slurry emptying system: mainly by accident slurry tank, an absorption tower area set puddle, pulping region set puddle, gypsum dewatering area sump composition, satisfy the system maintenance, washing needs.
3 process optimization
Swirl red tower of wet limestone gypsum method of sintering flue gas desulfurization technology since 2008 in headquarters of Baosteel No.3 sintering machine to use, after three years of operation to explore, the process do further optimization, and by the end of 2011 in the headquarters of Baosteel No. 2 sintering machine again should be used, the operation is good.
3.1CEMS
CEMS (ContinuousEmissionMonitoringSystem) the flue gas emission continuous monitoring system, is composed of monitoring subsystem of gaseous pollutants, particulate matter monitoring subsystem, flue gas parameters monitoring subsystem and data acquisition and processing and communication system. CEMS measurement of the original flue gas (inlet flue gas) includes the amount of flue gas, flue gas temperature, flue gas pressure, dust, SO2, NOx and so on. The set of data for sintering raw gas state parameters, on the one hand must be real-time transmitted to the environmental protection department of the government audit, on the other hand is also vital for desulfurization process control, especially in sintering condition is abnormal, flue gas temperature and pressure directly determine desulphurization system can afterwards continued normal operation. Therefore, the stability and authenticity of CEMS data detection is particularly critical. Headquarters of Baosteel No.3 sintering machine desulfurization facilities due to space limitations, the layout of the whole device is very compact, raw flue gas was relatively short, there is phenomenon of turbulent flow, the inlet flue gas (flue of raw) CEMS measurement value fluctuation caused by and for environmental monitoring and desulfurization process control adversely affected. In 2011, Baosteel headquarters in Supplement No. 2 sintering machine desulfurization facilities, appropriate to extend the raw flue gas pipe (compared to the No.3 unit desulfurization system, more than 10 meters long), weakening of the original flue gas turbulence phenomenon, to ensure the accuracy of the entrance of CEMS measurement.
3.2 cooler
Cooler is one of the three major equipment of limestone gypsum desulphurization facilities. Cooler in the cooling system, the first level by gas, cooling water, cooling water cooling water pump pressurized by six cooling aerosol spray gun and compressed air to mix and atomize downstream spray to sintering flue gas; the second stage of the absorption tower of limestone slurry cooling, limestone slurry after slurry cooling pump pressure, through 10 slurry cooling branch pipe spewing.
There are two types in the bottom of the cooler, as shown in figure 2.
Type A: two recesses are cooling water and slurry collecting part, cooling water pipes by gravity into the waste water tank, cooling slurry is piped returned to the absorption tower.
Type B: cancel the water cooling outlet, the and secondary slurry cooling export merged together through a pipeline returned to the absorption tower, a cooling water along the flow process of the bottom of the cooler can be washing slurry cooling. However, flushing water pipes must be installed at the periphery of the cooler and at the bottom of the dry and wet interface. The washing water is best to use the water in addition to the fog, so that the washing process can be included in the process of removing the mist, the effect is relatively ideal.
From the point of view of the operation performance, type a can completely avoid the cooler at the bottom of the accumulated material phenomena, and type B can will be at the bottom of the gradient further increased, the accumulated material phenomenon is eliminated.
In addition, the layout of the two level slurry cooling duct is also critical. If slurry cooling duct from the bottom to the top of the arrangement, the outage desulphurization facilities slurry cooling can be under the action of gravity return to the duct, not being left slurry accumulation blocked slurry cooling branch pipe, but the arrangement is not convenient for construction and daily maintenance work; and cooling the advantages and disadvantages of slurry duct arranged from top to bottom is just the opposite. The best solution is: in each root slurry cooling branch pipe is arranged under the flue gas to flow with the same cooling nozzle, so that the layout of the slurry cooling duct from top to bottom, can not be blocked, and convenient construction and daily maintenance.
3.3 absorption tower
The flue gas after two-stage cooling into absorption tower flue gas distributor, again through the aeration pipe sprayed into the absorption tower slurry pool, and the slurry pool surface formed stable drum bubble layer, in bubbling layer complete absorption of the desulfurization reaction, neutralization, oxidation, crystallization process. After the purification of flue gas through the upper and lower partitions between the riser into the mist. A flushing device is arranged on the upper and lower part of the absorption tower and the upper part of the upper part of the absorption tower, and the upper and lower parts of the partition plate are arranged on the upper part of the absorption tower. The flushing water of the upper baffle plate flows through the reflux pipe between the upper and lower partitions to the absorption tower slurry pool. Therefore, in the absorption tower between the diaphragm is 44 net emission of flue gas ascending pipe, and 106 root partition flushing water return pipe, on the bulkhead between the pipe lined, to flue gas carrying liquid and dust deposition created conditions. With the passage of time, they formed a relatively hard lumps, and in operation process for supersaturated high temperature flue gas continuous erosion may fall at any time, damaged bulkhead flushing water duct or pipe, leading to the diaphragm flushing failure, cause local product material and aeration pipe blockage, bring security risks but also to the maintenance operations. This problem is particularly prominent in the three sintering desulfurization system. After the study, cut out part of the refluxing pipe between the diaphragm, the problem has been effectively solved. Therefore, in the construction of two sintering desulphurization facilities, the reflux pipe which is completely removed from the upper partition plate is eliminated. Practice has proved that this optimization scheme is completely feasible and effective.
Need to explain is that of absorption tower body of the annular reinforcing rib type selection should be paid more attention to, especially the characteristic of wet desulphurization chimney rain "of equipment corrosion is very serious, so the annular stiffener I-steel and channel steel should be used, to avoid rain accumulation of absorption tower body corrosion.
3.4 slurry supply and evacuation
Baosteel headquarters limestone - gypsum desulfurization process using the mud cake as a desulfurization agent, in order to waste treatment of waste. However, due to the stacking and transportation and other links are not controlled, mud cake is inevitably mixed with debris, resulting in slurry and slurry pipeline easy to plug. Even by discharging pool, the puddle, accident slurry tank emptying and set up suitable pore size filter, blocking times decrease, but still have occurred, caused many adverse effects control on the desulfurization process, desulfurization rate is not high, slurry spillover. Therefore, in the second sintering desulfurization facilities in the design process, communicating the second and third sintering flue gas desulfurization facilities for headbox and accident slurry tank to in the pipeline jam cause among a set of desulfurization facilities not for slurry, a slurry discharge for emergency treatment, to ensure the stability of the control of the desulfurization process.
In addition, three of sintering flue gas desulfurization facilities absorption tower slurry emptying is generally will tower serous fluid in a first emission to absorption tower sump. The sump pump to send the past so slurry tank. This process takes about 12 hours, which seriously affects the synchronous operation of desulphurization facilities. In view of this, two sintering flue gas desulfurization facilities by the slurry cooling pump absorption tower slurry emptying operation, the whole process only about 2 hours, not only saves the emptying time of grout, more important is to avoid the slurry settlement, to ensure that the next operation of slurry quality.
3.5 "chimney rain" control
"Chimney rain" phenomenon in the limestone - gypsum desulfurization of the "wet chimney" in the near - kilometer radius is particularly prominent, especially in winter more serious. Down to the ground of the chimney drops containing SO2, SO3 and gypsum slurry, dust and other impurities. SO2, SO3 reacts with water to form sulfuric acid or sulfuric acid, which causes the liquid drop to be acidic, which has certain pollution and damage to the buildings, the greening and the vehicles in the area.
GGH is widely used in the power industry to eliminate the "chimney rain", but the method is very easy to plug in the process of application, on the other hand, the sintering process can not meet the conditions of GGH. Therefore, how to control the sintering desulphurization facilities "chimney rain", weakening the harm is another problem faced by researchers. Baosteel technical staff has been committed to this research, that in the case can not improve the net flue gas emission temperature, can be reduced by reducing the flow rate of flue gas to control the chimney rain". Two kinds of schemes are proposed to choose, one is to enlarge the space of the top of the absorption tower, the two is to lengthen the flue between the outlet and the chimney. After the application of the second schemes in a sintering desulphurization facility at Baosteel Group, the results are quite remarkable. At present, the two sintering desulfurization mainly from the operation to reduce the flue gas flow rate, a moderate increase in the net flue gas temperature, etc. to control the occurrence rate of "chimney rain".
4 operation practice
Baosteel headquarters two sintering desulphurization facilities after a series of process adjustment and optimization, the system operating conditions are significantly better than the three sintering desulphurization facilities, in 2012, the key operational parameters are listed in table 1.
As can be seen from table two, 1 SINTERING desulphurization facilities net flue gas SO2 emission concentration of only 50mg/Nm3, far less than the state of the country in October 1, 2012 the newly issued new enterprise 200mg/Nm3 emissions requirements. Comprehensive desulfurization efficiency is up to 84.6%, the annual cumulative emission reduction of SO25000 tons, the regional environment has been significantly improved.
Original title: [technical literature] Baosteel two sintering flue gas desulfurization process optimization and operation practice