Report on the PCDD/PCDF/CO-PCB reduction measures for the steel manufacturing electric arc furnaces in Japan, and the consequent effects

Transcription

1 Report on the PCDD/PCDF/CO-PCB reduction measures for the steel manufacturing electric arc furnaces in Japan, and the consequent effects Government of Japan June, 2, 2006 Situations of implementing the measures to reduce the PCDD/PCDF/CO-PCB emission from the steel manufacturing electric arc furnaces in Japan that are specified in the draft guidelines on BAT/BEP, and the consequent PCDD/PCDF/CO-PCB reduction effect were investigated, targeting 19 factories of 11 companies out of 38 non-integrated steel producers in Japan. This paper describes the facility outline, present situations of implementing technology in line with the draft guidelines on BAT/BEP actual situations of the PCDD/PCDF/CO-PCB emission, and the consequent reduction effects. 1. Outline of the steel manufacturing electric arc furnaces in Japan 1) Steel manufacturing electric arc furnaces a. Steel manufacturing electric arc furnaces Scrap is melted using electric arc at 4000 C. It is refined after removing impurity to make steel. There are two types of electric arc furnaces of DC and AC; however, all the target factories use the same type of melting system. Electrode To the off-gas dust collector Burner Oxygen pipe Arc at 4000 C Arc Molten steel Figure 1 Steel manufacturing electric arc furnace b. Process (1) Charging (2) Melting (3) Refining (4) Discharging Figure 2 Process flow 1

2 c. Dust collection system There are different types of dust collection systems for steel manufacturing electric arc furnaces: Independent off-gas system that consists of independent lines of a house dust collection line and a direct-suction line, which sucks off-gas directly from the electric arc furnace, and; Joint off-gas system that connects a direct-suction line to a house line to join off-gas together. In many case of remodeling the dust collection system, a dual-stage dust collection system is adopted, which passes off-gas through the existing direct-suction line first, and then joins it to the house dust collector inlet. The PCDD/PCDF/CO-PCB was measured after the dust collector in both the direct-suction line and the house line. (Refer to Appendix-1) House dust collector Electric arc furnace Combustion tower Cooling tower Direct-suction dust collector Figure 3-a Independent off-gas system: A house dust collector is independent from a direct-suction line dust collector. House dust collector Electric arc furnace Combustion tower Cooling tower Figure 3-b Joint off-gas system: A direct-suction line is connected to a house dust collector. 2) Scrap to be used Purchased scrap occupies about 90%, which includes heavy scrap, new cutting scrap, machining chip, and shredder scrap. With exception of new cutting scrap, such purchased scrap contains chlorine; therefore, it is considered as a major cause of PCDD/PCDF/CO-PCB generation. The chlorine is contained in various substances adhered to the scrap like paint, which is hardly screened out. From the 2

3 viewpoint of enhancing recycles of resources, however, it is necessary for the industry to accept the scrap that contains a certain level of substances adhered (Table 1). Table 1 Percentage of the scrap by type and chlorine (Cl) content Type (source) Percentage (%) *1 Example of Cl content (%) *2 Heavy scrap New cutting scrap 15 0 Machining chip Shredder scrap Others 9 Note) *1 Investigated by the Japan Iron and Steel Federation *2 Estimated by a non-integrated steel producer 3) Factors to emit PCDD/PCDF/CO-PCB The electric arc furnaces use electric power, a clean energy, as a main heat source; however, purchased scrap including waste scrap and working scrap is coated or adhered with oil, paint, plastics, etc. These are considered as a cause of PCDD/PCDF/CO-PCB generation. Scrap is melted using electric arc at 4000 C, where the furnace wall is red heated, and the furnace temperature reaches a high temperature above 1000 C; therefore, PCDD/PCDF/CO-PCB is hardly formed in the furnace. Re-synthesizing in the off-gas cooling process is considered as the prime cause of forming PCDD/PCDF/CO-PCB. 2. Present situations of implementing the PCDD/PCDF/CO-PCB reduction measures specified in the draft guidelines on BAT/BEP The PCDD/PCDF/CO-PCB reduction measures for steel manufacturing electric arc furnaces specified in the draft guidelines on BAT/BEP, and the present situations of implementing those in 19 factories of the environmental committee under the Non-integrated Steel Producer s Association are described below. It is summarized by factory in Appendix 2. 1) Primary measures to reduce PCDD/PCDF/CO-PCB General operating practices All the factories have prepared own operation procedures. Optimum environment-, working-, and maintenance- standards have been established. Raw material quality All the factories have prepared own acceptance inspection standards for pollution prevention. They screen incoming scrap according to the standards, and return the scrap that contains significant oil and/or plastics. However, purchased heavy scrap varies in quality depending on its source. Scrap is sorted by source for controlled blending in the scrap industry; however, adhered substances like paint are hardly removed. Electric arc furnace operation All the factories have prepared own operation manual to prevent off-gas from leaking out of the furnace. Off-gas conditioning 7 factories out of 19 cool down the off-gas rapidly below C (by installing a gas 3

4 cooler), where the temperature is controlled below 220 C. Continuous parameter monitoring All the factories continuously monitor the temperature at the dust collector inlet to ensure optimum operation of the off-gas conditioning system. 2) Secondary measures to reduce PCDD/PCDF/CO-PCB Off-gas collection All the factories have installed a house dust collector that prevents off-gas from leaking out of the house, where a dust collection efficiency more than 98% has been achieved. Fabric filters Filters are made of fabric, or synthetic resin (Tetoron, etc.). All the factories are engaged in improvement, maintenance, and management of the filter fabric, including optimization of the backwash reverse filtration cycle, and improvement of filter materials (changing from glass fiber to synthetic resin). Filter materials and preventive maintenance have been examined to prevent any dust from being discharged. In addition, the off-gas suction efficiency has been improved. Post-combustion of off-gas All the factories installed a combustion tower in the past. However, it is for afterburning the refinement reaction gas (main composition: CO) generated in the furnace by mixing it with air, but not by adding extra oxygen or fuel. The furnace temperature seems to be high enough, i.e., 1600 C in operation, to decompose PCDD/PCDF/CO-PCB in the furnace. It is not always necessary to raise the furnace temperature by adding oxygen into the combustion tower for enhancing combustion. Adsorbent injection None of the factories use calcium hydroxide or other absorbents to reduce the PCDD/PCDF/CO-PCB emission. However, it is now under testing in a factory. The absorbent injection seems not to be used so extensively. The reason is; a) It is necessary to prevent red heated scrap and charcoal from scattering, because any fire in the dust collection system may cause explosion. b) It is necessary to decrease temperature at the bag filter inlet because coal-base activated carbon may serve as a reaction catalyst for re-synthesizing. c) Injecting absorbent into the gas with dusts of a high concentration may result in a low absorption efficiency. (In order to improve the absorption efficiency, reduce the activated carbon consumption, and maintain PCDD/PCDF/CO-PCB at a low level, it is necessary to reduce the dust concentration.) d) Cost of the activated carbon is high. (It is necessary to reduce the unit consumption). Minimize solid waste generation All the factories have recycled dusts as much as possible. They comply with the applicable regulations related to the waste treatment and cleaning when they dispose some of them. Minimize waste water All the factories have used cooling water in a closed system. They appropriately treat the water used for preventing air pollution before discharging it. 3. Actual situations of the PCDD/PCDF/CO-PCB emission, and reduction effect of the measures Actual situations of the PCDD/PCDF/CO-PCB emission, and reduction effects of the measures are summarized below based on the questionnaire survey results, targeting 19 factories of 11 environment 4

5 committee companies of the Non-integrated Steel Producer s Association. Reduction effects of the measures are evaluated for the case of implementing a single measure, separately from the case of implementing two or more measures at a time, since some factories have implemented two or more measures at a time. Measurements were made in accordance with JIS K0311, using a high-resolution gas chromatograph mass spectrometer. The TEQ was calculated using WHO-TEF (1998). 3-1 Target period and PCDD/PCDF/CO-PCB reduction measures 1) Target period Years 2000 and 2004 were selected as the target period. This was determined in consideration of the fact that non-integrated steel producing companies implemented the major PCDD/PCDF/CO-PCB reduction measures when the emission standard was tightened in 2002 under the PCDD/PCDF/CO-PCB Prevention Special Measures Law. 2) Target PCDD/PCDF/CO-PCB reduction measures Among the PCDD/PCDF/CO-PCB reduction measures, Cool down of the off-gas, Change to the joint off-gas system, Disuse of SPH, and Other operational efforts were targeted. These items were selected for the reason described below. Where, Other operational efforts means all the measures including those specified in the draft guidelines on BAT/BEP, which had been applied continuously by 2004, except cool down of the off-gas, change to the joint off-gas system, and disuse of SPH. In particular, it includes improvement of the dust collection efficiency, optimization of the existing bag filter cleaning cycle, optimization of the continuous monitoring of parameters, etc. These items should be achieved by operational efforts including improvement of the existing equipment; however, it seems to contribute to the PCDD/PCDF/CO-PCB reduction. The PCDD/PCDF/CO-PCB contents before and after the measures were clarified only for the item of Cool down of the off-gas, among all the PCDD/PCDF/CO-PCB reduction measures specified in the draft guidelines on BAT/BEP. By 2000 all the factories had implemented; General operating practices, Raw material quality, Electric arc furnace operation, and Continuous parameter monitoring, among the primary measures specified in the guideline draft, and; Off-gas collection, Fabric filters, Minimize solid waste generation, and Minimize waste water, among the secondary measures. For the reason described in 2. 2) above (Secondary measures to reduce PCDD/PCDF/CO-PCB), on the other hand, none of the factories had implemented Post-combustion of off-gas, and Adsorbent injection, among the secondary measures. The measure item of Change to the joint off-gas system was not specified in the draft guidelines on BAT/BEP; however, it was selected as a target of this analysis because some factories had implemented it combined with Cool down of the off-gas (refer to Table 4, and Figure 6). This item does not fall in a category of cooling down rapidly using a gas cooler; therefore, it was separated from the item of Cool down of the off-gas specified in the BAT/BEP guideline draft. The measure item of Disuse of the SPH was not specified in the draft guidelines on BAT/BEP; however, it was selected as an analysis target because some factories had implemented it combined with Cool down of the off-gas (refer to Table 4, and Figure 6). Where, the SPH (Scrap Pre-Heater) preheats scrap up to C before charging it to 5

6 the furnace, using effectively the off-gas heat, which occupies about 20 to 30% of the whole heat output from the electric arc furnaces. 3-2 Overall summary The PCDD/PCDF/CO-PCB concentration before and after implementing the PCDD/PCDF/CO-PCB reduction measures and the amount of investment are shown in Table 2. The reduction measures specified in the draft guidelines on BAT/BEP have been implemented to the steel making electric arc furnaces in Japan by investing in equipment as far as affordable at present; however, only 2 factories out of 19 (about 10%) achieved the value below 0.1ng-TEQ/Nm3 (APL value of the steel making electric arc furnaces) in 2004, both of which are the same factories in 2000 and In comparison of the emission concentration in all the 19 factories between before and after implementing the reduction measures, it was reduced by 84.0% on average, from the average of 2.62 ng-teq/nm3 to 0.42 ng-teq/nm3 (Table 3). Most factories achieved the emission concentration in the range of 0.1ng-TEQ/Nm3 to 0.5ng-TEQ/Nm3 after implementing the reduction measures (Figure 4). In the last decade (including 2004 and later), a total amount of 6,000 million yen was invested in equipment in 19 factories to reduce PCDD/PCDF/CO-PCB (for detail refer to Appendix-2). Table 2 PCDD/PCDF/CO-PCB concentration before and after implementing the PCDD/PCDF/CO-PCB reduction measures, and amount of investment PCDD/PCDF/CO-PCB concentration (ngteq/nm3) Number of factories () before implementing (in 2000) Number of factories () after implementing (in 2004) Amount of investment average1 5 or more 3 (16) 0 (0) 1 to 5 9 (46) 1 (5) 150 million yen 0.5 to 2 (11) 2 (11) 110 million yen 0.1 to (16) 14 (73) 290 million yen less than (11) 2 (11) Note 1) Data from 19 factories of 11 non-integrated steel producers Note 2) It targets the measures implemented in 2000 through 2004, which includes part of those specified in the draft guidelines on BAT/BEP. 1 Amount of investment (average) means the average of the amount of investment for reduction measures implemented in 2000 through

7 Figure 4 Changes of the emission concentration before and after implementing the reduction measures (overall) 3-3 PCDD/PCDF/CO-PCB reduction effects by a single measure and two or more measures Changes of the emission concentration before and after implementing a single measure are shown in Table 3, while changes of the emission concentration before and after implementing two or more measures are shown in Table 4. The emission concentration was reduced by 80.0% to 87.2% in the factories that implemented a single measure of cooling down the off-gas, changing to the joint off-gas system, or disusing the SPH. It was reduced further by 96.1% to 96.3% in the factories that implemented two or more measures. Figures 5 and 6 prove that a higher reduction rate was achieved by implementing two or more measures. 7

8 Table 3 Changes of the emission concentration before and after implementing the reduction measures (effects of a single measure) Cool down of the off-gas Change to the joint off-gas system Disuse of the SPH Other operational efforts Average Standard deviation Variance Number of samples Pearson s correlation Difference from the hypothetical average Degree of freedom P (T <= t), one side t boundary value, one side Significance - Yes Yes Yes Yes Reduction rate () Target factory (Appendix-2) N B, E, H, P G, J C, D, F, K, L, M, O, Q, R, S Note 1) Evaluated using t-test (level of 5) Note 2) Reduction rate after implementing the measures (in 2004) (%), from the average PCDD/PCDF/CO-PCB concentration before implementing the measures (in 2000) Total A to S Figure 5 Changes of the emission concentration before and after implementing the reduction measures (effects of a single measure) 8

9 Table 4 Changes of the emission concentration before and after implementing the reduction measures (effects of two ore more measures) Cool down of the off-gas and change to the joint off-gas system Cool down of the off-gas and disuse of the SPH Total Average Standard deviation Variance Number of samples Pearson s correlation Difference from the hypothetical average Degree of freedom P (T <= t), one side t boundary value, one side Significance - - Yes Reduction rate () Target factory (Appendix-2) I A A to S Note 1) Evaluated using t-test (level of 5) Note 2) Reduction rate after implementing the measures (in 2004) (%), from the average PCDD/PCDF/CO-PCB concentration before implementing the measures (in 2000) Figure 6 Changes of the emission concentration before and after implementing the reduction measures (effects of two ore more measures) 9

10 3-4 Cool down of the off-gas 3 factories implemented the reduction measure of cooling down the off-gas in 2000 through Among them, 2 factories implemented two or more measures. The emission concentration was reduced by 96.1% in the factory that implemented the measures of cooling down the off-gas and disusing the SPH; while it was reduced by 96.3 in the factory that implemented the measures of cooling down the off-gas and changing to the joint off-gas system (Table 4). Examples of implementing two or more measures are listed in Table 5. Figure 7 Changes of the emission concentration before and after implementing the reduction measure of cooling down the off-gas (effects of a single measure) Figure 8 Changes of the emission concentration before and after implementing the reduction measure of cooling down the off-gas (effects of two or more measures) 10

11 Table 5 Examples of implementing two or more reduction measures PCDD/PCDF/CO-PCB PCDD/PCDF/CO-PCB Factory Invented in: concentration (ng-teq/nm3) reduction measure I Cool down of the off-gas + Change to the joint off-gas system Cool down of the off-gas + Disuse of the SPH Before implementing 8.9 (in 2000) 8.5 (in 2000) After implementing 0.33 (in 2004) 0.33 (in 2004) Amount of investment 910 million yen 300 million yen Note) The factory symbols correspond to those used in Appendix-2. The toxic equivalent factor was calculated using WHO-TEF (1998): Measurements were made in accordance with JIS K0311, using a high-resolution gas chromatograph mass spectrometer. 3-5 Change to the joint off-gas system 5 factories implemented the reduction measure of changing to the joint off-gas system in 2000 through Among them, 1 factory implemented also the measure of cooling down the off-gas. The emission concentration was reduced by 80.0% on average in 4 factories that implemented only the measure of changing to the joint off-gas system (Table 3). Most factories achieved the emission concentration in the rage of 0.1 to 0.5ng-TEQ/Nm3 after implementing the measure (Figures 9 and 10). It was 0.79ng-TEQ/Nm3 on average in the factories that implemented a single measure, while it was 0.33ng-TEQ/Nm3 in the factory that implemented two or more measures (Tables 3 and 4). Figure 9 Changes of the emission concentration before and after implementing the reduction measure of changing to the joint off-gas system (effects of a single measure) 11

12 Figure 10 Changes of the emission concentration before and after implementing the reduction measure of changing to the joint off-gas system (effects of two or more measures) 3-6 Disuse of the SPH 3 factories implemented the reduction measure of disusing the SPH in 2000 through Among them, 1 factory implemented also the measure of cooling down the off-gas. The emission concentration was reduced by 86.0% on average in 2 factories that implemented the measure of disusing the SPH (Table 3). These factories achieved the emission concentration in the rage of 0.1 to 0.5ng-TEQ/Nm3 after implementing the measure (Figures 11 and 12). It was 0.35ng-TEQ/Nm3 on average in the factories that implemented a single measure, while it was 0.33ng-TEQ/Nm3 in the factory that implemented two or more measures (Tables 3 and 4). Figure 11 Changes of the emission concentration before and after implementing the reduction measure of disusing the SPH (effects of a single measure) 12

13 Figure 12 Changes of the emission concentration before and after implementing the reduction measure of disusing the SPH (effects of two ore more measures) 3-7 Other operational efforts 10 factories did not implement any 3 measures of cooling down the off-gas, changing to the joint off-gas system, and disusing the SPH in 2000 through 2004 (Table 3). The emission concentration was reduced by 67.7% in these 10 factories, which are grouped as other operational efforts. Most factories achieved the emission concentration in the rage of 0.1 to 0.5ng-TEQ/Nm3 after implementing the measure (Figure 13). It was 0.32ng-TEQ/Nm3 on average (Table 3). Figure 13 Changes of the emission concentration before and after implementing the reduction measure of other operational efforts 13

14 4. Conclusion According to the questionnaire survey results targeting 19 factories of 11 environment committee companies of the Non-integrated Steel Producer s Association, almost all the reduction measures specified in the draft guidelines on BAT/BEP were implemented. The emission concentration was reduced 84.0% on average from those before implementing the measure. The average concentration was 0.42 ng-teq/nm3. Only 2 factories (10% of all targeting factories) achieved the APL value below 0.1ng-TEQ/Nm3 at this stage. The emission concentration was reduced by 80% to 87.2% in the factories that implemented a single measure of cooling down the off-gas, changing to the joint off-gas system, or disusing the SPH in 2000 through This analysis revealed that disusing the SPH was effective to reduce PCDD/PCDF/CO-PCB; however, some factories in a snowfall area might find it difficult to implement the measure of disusing the SPH from the viewpoint of safety, because they have to remove snow or ice on scrap that may result in a phreatic explosion in the furnace. The emission concentration was reduced by 96% or more in the factories that implemented two or more measures (cool down of the off-gas and change to the joint off-gas system, or cool down of the off-gas and disuse of the SPH), where a higher reduction rate was achieved than in the factories that implemented a single measure of cooling down the off-gas. Any measures seemed to be effective to reduce PCDD/PCDF/CO-PCB; however, a higher reduction rate was achieved by implementing two or more measures rather than by implementing a single measure. The PCDD/PCDF/CO-PCB emission from the steel manufacturing electric arc furnaces reflects the situation of the overall recycling system in each individual country, including the scrap recycling level, electric arc furnace equipment level, operational level, product line, and final dumping sites. 14