Assessing CO 2 mitigation potential by technological improvement in China s chemical industry

Transcription

1 Assessing CO 2 mitigation potential by technological improvement in China s chemical industry Bing Zhu a,b, Wenji Zhou a, Shanying Hu a, Qiang Li a, Charla Griffy-Brown c, Yong Jin a a Department of Chemical Engineering, Tsinghua University, Beijing , China b International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria c Graziadio School of Business, Pepperdine University, Los Angeles, CA 90045, USA of Prof. Bing Zhu: bingzhu@tsinghua.edu.cn of Mr. Wenji Zhou: wenji.zhou@gmail.com

2 Abstract The increasing trend of China s CO 2 emissions is primarily driven by the fast expansion of high energy-intensive sectors including the chemical industry. This study attempts to investigate energy consumptions and CO 2 emissions in the processes of chemicals production in China through calculating the amounts of CO 2 emissions and estimating its reduction potential in the near future. The research is based on a two-level perspective which treats the entire industry as Level 1 and six key sub-sectors as Level 2, including coal-based ammonia, calcium carbide, caustic soda, coal-based methanol, sodium carbonate, and yellow phosphorus. Three scenarios with different technological improvements are defined to estimate the emissions of the six sub-sectors and analyze the implied reduction potential in the near future. The results highlight a pivotal role that mandatory regulated administration could play to control the CO 2 emissions through promoting average technology performances in this industry. Keywords China s chemical industry, CO 2 emissions, CO 2 reduction potentials 1. Introduction As one of the largest chemical producers in the world, China has experienced remarkable growth occurred in the chemical industry during the short period from 2000 to 2007, which directly spurred the total energy consumption and associated CO 2 emissions nationwide. According to the data reported from the International Energy Agency [1,2], China s total CO 2 emissions by fossil fuel consumption increased sharply at an annual growth rate above 10% to 6.07 billion tons during the period from 2002 to This trend imposes enormous pressure on China s government and society to meet the challenge of climate change. To address this issue, a broad sector-based study of measures aiming at controlling CO 2 emissions in those typical heavy industries should be considered as one of the most important topics during the process of designing the CO 2 -mitigation plan. Some researches attempted

3 to offer sector-based analysis of CO 2 emissions and the corresponding mitigation approaches for specific industries [3-5]. Not surprisingly, the results showed that the potential for these industries varied. But the common interesting finding was that in the short term, by 2015 or 2020, the carbon intensities for each sector investigated would only decrease by less than 40% even under the most favorable scenarios, which might not by itself meet the target set by the administration. This raises one important question: how far we can go to reduce CO 2 emissions in China s industrial sector by implementing more energy-saving and low carbon technologies, given that the sub-sectors are under different stages of development. Therefore this kind of study must be extended into other key industrial sectors such as the chemical industry, and eventually obtain a comprehensive understanding of the entire manufacturing sector as well as subdividing the country s carbon intensity target for more effectively addressing the problem. Chemical manufacturing in China, unlike the single-product industries, is a far more complicated system supplying various types of raw material, fertilizer, coating, pesticide, synthetic material etc. for China s high economic growth. In excess of 40 thousand chemicals covering the fundamental raw materials, including fertilizer, coating, pesticide and synthetic material, exist in the industry. Consequently, it is extremely difficult to survey the industry, perform accurate calculation and analysis of related studies regarding energy consumption and CO 2 emissions assessment. In this research, we not only calculate the CO 2 emissions of the whole industry, but also select six key sub-sectors (coal-based ammonia, calcium carbide, caustic soda, coal-based methanol, sodium carbonate, and yellow phosphorus) to go deep inside specific producing processes, investigate their CO 2 emission patterns and assess reduction potentials through technological improvement. The content is organized as follows: after this introduction, Section 2 explains the conceptual framework of this research and defines the boundary for the calculation and potential assessment. Section 3 calculates the emission amounts from the perspective of two-levels, and

4 emission factors for each of the six key sub-sectors are also estimated. Section 4 assesses the reduction potentials through scenario analysis which takes into account different technology improvements in the near future. Finally, Section 5 concludes and discusses the administrative efforts needed in the process of controlling CO 2 emissions in this industry in the face of the fast development expected in the near future. 2. Framework and boundary definition 2.1 Framework We conducted the research in a combined way for two levels, as presented in the framework of the research in Fig.1. Level 1 covers the entire industry. Level 2 covered the specific sub-sectors of the industry using a bottom-up approach. Six key sub-sectors, i.e., coal based ammonia, calcium carbide, caustic soda, coal-based methanol, sodium carbonate, and yellow phosphorus, were selected according to their output and energy requirement, representing a large quantity of CO 2 output and being appropriate industry proxies. In principal, CO 2 released from chemical production could be categorized as resulting from two main sources. One occurs in the conversion process from feedstock to the final product, defined as process-related emission in this research. The other results from fuel combustion for heat supply, defined as combustion-related emission. The six key sub-sectors are also divided into two categories based on their characteristics of CO 2 emission pattern. The process-related emission category includes four chemicals, coal-based ammonia, calcium carbide, coal-based methanol, and sodium carbonate; the other two, yellow phosphorus and caustic soda, belong to the combustion-related emission category.

5 Level two: Key sub-sectors Analysis of CO 2 emission reduction potential Level one: The whole industry Ammonia Calcium carbide Process-related CO 2 emission Scenario 1: baseline Chemcial Industry + Sodium carbonate Methanol Calculation of CO 2 emission amount Scenario 2: Low technology improvement rate Yellow phosphorus Scenario 3: High technology improvement rate Caustic soda Combustion-related CO 2 emission Fig. 1. The framework of the study To calculate the CO 2 emission amount for each sub-sector, detailed information regarding technology mix, energy performance and fuel requirement are surveyed. Based on this calculation, their respective reduction potentials are assessed by comparing the scenario with low technology improvement rate (Scenario 2), or with high technology improvement rate (Scenario 3), and a baseline scenario (Scenario 1) in the near future. Consequently, the contribution of technological improvement to the reduction of CO 2 emissions in China s chemical industry is discussed. 2.2 Method According to the status of China s chemical manufacture and the extent of the associated data that are available, we employ an emission factor-based method to estimate the total CO 2 emission at an industrial level. The basic equation for estimating emissions at level one is: E = EF FC (1) CO2 i i i Where E CO = CO 2 2 emission amount, ton, EF = emission factor of the fuel type i, ton i CO 2 /ton fuel, FC i = amount of the fuel type i consumption, ton. Level 2 covers specific chemical production. In general, multiple techniques always coexist for one chemical manufacture with various performances. Thus, we calculated the CO 2 emissions based on techniques employed, which also facilitated the

6 assessment of the mitigation potentials of CO 2 emissions through the technological improvement of these techniques. At Level 2, the equation is formulated as: E = EP PA (2) mco, 2 mj, mj, j Where E m, CO =CO 2 2 emission amount of the chemical m, ton, EP m, j= CO 2 emission of the technique type j for per unit product m, ton CO 2 /ton product, PA m, j= production amount of chemical m through technique type j, ton. The parameter of EP m, j which features the CO 2 emission of each chemical is then calculated through: EP = EF FC (3) mj, mk, mk, k Where EF mk, = emission factor of the fuel type k consumed for producing chemical m, FC mk, = amount of the fuel type k consumption for producing chemical m. 2.3 System boundary The calculation at Level 1 focused on the entire industry which covers a broad range of chemical categories primarily including raw chemical materials and chemical products. The petroleum industry, comprised of oil refinery, natural gas processing and their derivatives, is not taken into account in this study, because we intend to give more emphasis to coal utilization and its resulting CO 2 emissions for the industry considering the dominance of coal in China s energy supply mix. The calculation involves various energy categories for chemicals production. Besides coal and its main varieties, for instance raw coal, cleaned coal, and washed coal, other final fuel types including oil, natural gas or their varieties, and electricity are also used. Instead of investigating all of these energy categories fueled for the industry, we choose coal total, coke, petroleum products total, natural gas, heat and electricity as six main representatives of all the energy sources that release CO 2, to avoid redundant estimation of emission factors of subdivided energy types which accurate values cannot be obtained based on current data conditions.

7 3. CO 2 emissions in China s chemical industry 3.1 CO 2 emissions at Level 1 The CO 2 emission factors of the six main fuel types were collected or estimated, as summarized in Table 1. The factors for raw coal, coke, crude oil and natural gas were obtained from the National Development and Reform Commission of China (NDRC) [15], the factor for electricity is taken in the average value of the six regional baseline emission factors reported by NDRC [15]. There is no direct emission factor associated with steam consumption is reported yet, so we estimated it by considering the steam boiler efficiency, as explained in Table 1. Table 1 Emission factors for different energy forms in China s chemical industry in 2007 Coal Coke Oil Emission factor tons CO 2 /ton coal tons CO 2 /ton coke tons CO 2 /ton oil Estimation Calculated from [15] Calculated from [15] Calculated from [15] Natural gas Electricity Steam(low pressure) Emission factor tons CO 2 /km tons CO 2 /ton tons CO 2 /MWh natural gas steam Calculated from [15], Estimation Calculated from [15] The emission factor already included the shares of other power generation forms besides coal-fired such as hydro and nuclear supplying electricity for China s grid in The caloric value of low pressure steam is taken as kgce/ton steam, and the efficiency of coal converting to steam is taken as CO 2 emissions from 2000 to 2007 in the entire industry and the mix of the five energy categories with their resulting emissions are presented in Fig. 2. The results show that during these eight years, the amount of CO 2 emissions doubled from 323 million tons in 2000 to 678 million tons in 2007, accounting for 10.6% and 11.3% of the national total respectively (the national emission amounts are from [2]). This trend is expected to continue in the near future, which imposes a great deal of pressure on China s society to control GHG emissions and environmental pollution. The six energy resources had various contributions to the total CO 2 emissions of the industry.

8 Electricity resulted in the most CO 2 emissions among the six, about 41.5% of the total in Coal and coke together comprised almost 30%, and heat uses which were also supplied by coal combustion offered 10%, while the shares of oil and natural gas were only 14% and 7.6% respectively coal coke oil natural gas heat electricity Fig. 2 CO 2 emissions in China s chemical industry and the compositions of the five final energy categories-resulted emissions from 2000 to 2007(million tons). (Note: the original energy consumption data is from [6], the emission factors for electricity in different years are obtained from NDRC annual report [15] ) 3.2 CO 2 emissions at Level 2 Table 2 summarized the CO 2 emission sources in the process of the six chemicals manufacturing and the CO 2 emissions per ton product which are calculated by averaging emissions from different technical routes of one sub-sector. In line with the energy consumption, producing yellow phosphorus resulted in the most CO 2 emissions, which was as much as tons for per unit product due to its high electricity consumption. Coal-based synthetic ammonia and calcium carbide possessed multiple CO 2 emission sources over the entire process and thus are also CO 2 -intensive. Coal-based methanol, produced by processes similar to ammonia production (in fact half of coal-based methanol in China were co-produced with ammonia in the same unit), yielded less CO 2 as part of the carbon content converted into the final product. Caustic soda and sodium carbonate, though rarely emitted CO 2 directly in their manufacturing process, were also associated with certain CO 2 emissions because of their electricity and steam uses.

9 Table 2 CO 2 emissions in the six sub-sectors in 2007 CO 2 emission patterns Techniques employed CO 2 emission per unit CO 2 emission of the production in 2007 sub-sector in 2007 (tons CO 2 /ton) (million tons) Ammonia (coal Process-related emissions: based) Coal gasification; Shift reaction; Combustion-related emissions: Coal combustion; Electricity use (indirect) calcium carbide Process-related emissions: Cement preparation (indirect) Combustion-related emissions: Treatment of CO generated; Electricity use (indirect) Caustic soda Combustion-related emissions: Electricity use (indirect); Steam use (indirect) Methanol Process-related emissions: (coal-based) Coal gasification; Shift reaction; Combustion-related emissions: Coal combustion; Electricity use (indirect) Sodium carbonate Process-related emissions: Fugitive emissions Combustion-related emissions: Electricity use (indirect); Steam use (indirect) Yellow phosphorus Combustion-related emissions: Electricity use (indirect) Large-scale: Lurgi; Texco; Middle and small-scale: UGI; Open furnace; semi-covered furnace; closed furnace Diaphragm process Ion membrane process Large-scale: Lurgi; Texco; Middle and small-scale: UGI; Ammonia-soda process (Solvay process) Combined-soda process (Hou's process) Electric arc furnace: 3000~12000kVA kva electric arc furnace

10 (Note: energy consumption data are from [6-14])

11 ammonia 27% calcium carbide 11% caustic soda 10% methanol 4% sodium carbonate 4% other 42% yellow phosphorus 2% Fig. 3 CO 2 emissions shares of the sub-sectors in China s chemical industry in Figure 3 presents the shares of the six sub-sectors for the entire chemical industry in 2007 regarding aggregated CO 2 emissions. Among the six, coal-based ammonia, calcium carbide and caustic soda constituted relatively large proportions of CO 2 emissions in China s chemical industry in 2007, as they possessed larger output quantities. While coal-based methanol, sodium carbonate and yellow phosphorus made up less. The total of the six reached as high as 397 million tons, accounting for about 58% of the whole industry, or 6.6% of the national total. As a result, these six chemicals represented the most CO 2 -intensive fields in China s chemical industry and should be considered the most important sectors with regards to energy saving and CO 2 mitigation. 4. Potential analysis As shown in Table 2, technologies with small scale and low efficiency were widespread in the six sub-sectors in 2007, which implies tremendous potential in these sub-sectors for energy saving and CO 2 emissions reduction. Three scenarios are defined to analyze the potentials of CO 2 mitigation for the manufacturing of these chemicals in the near future in China. The time scope is set to 2015 which is the end of China s twelfth five-year period. Scenario 1: baseline In this scenario, levels and structures of the technologies employed in these

12 sub-sectors are assumed to remain similar to those used in 2007, which also means that energy performances and CO 2 emissions for per unit product will not change. The outputs of the six chemicals will continue to grow at an annual rate of 2%. Scenario 2: low technological improvement rate This scenario assumes that technical performance will improve to a small extent, and that domestically advanced technologies in 2007, representing the least energy requirements and CO 2 emissions in China currently, will be widely applied for producing those chemicals in As a result, the average levels of energy consumption and CO 2 emissions in 2015 are set as equal to those of domestically advanced levels in China in Scenario 3: high technological improvement rate This scenario assumes that technological improvements in the six sub-sectors can reach significant widespread achievements. In this scenario, we assume that the average levels of the technology performances in 2015 will be commensurate with best practices worldwide in 2007, implying a further improvement based on Scenario 2. Table 3 CO 2 emissions per unit product for the six sub-sectors in the three scenarios (ton CO 2/ton product) Scenario 1 Scenario 2 Scenario 3 Ammonia Calcium carbide Caustic soda Methanol Sodium carbonate Yellow phosphorus Based on the specifications defined above, CO 2 emissions for per unit production of the six sub-sectors were calculated for the three scenarios, as summarized in Table 3. CO 2 emissions of the six sub-sectors in the three scenarios were calculated and presented in Fig. 4. The results show that among the six, coal-based ammonia production will still emit highest CO 2 amount, reaching as high as 217 million tons in Scenario 1 without any technological improvement. The comparisons among the three

13 scenarios show that, in the low improvement rate scenario, coal-based ammonia and caustic soda have an advantage of reduction potential in terms of absolute quantity, with 19.9 and 17.7 million tons CO 2 respectively. However, if these reduction amounts are divided by Scenario 1, caustic soda and coal-based methanol have the largest potential proportion (in excess of 20%). In contrast, yellow phosphorus ranks last with the potential proportion of only 5.1%, implying that the energy performances of the domestic technologies in this sub-sector were at relatively even levels. In Scenario 3, the potential reductions for coal-based ammonia, calcium carbide and caustic soda jump to 46.4, 23.6 and 34.6 million tons, with proportions of 21.4% and 42.2% for each baseline. Coal-based methanol does not show this huge potential yet, as there are very few units employing coal as feedstock for methanol production in other countries besides China and thus it is difficult to make comparisons. Potentials for sodium carbonate and yellow phosphorus are also relatively small, but still remarkable if compared with their baselines in Scenario ammonia calcium carbide caustic soda methanol sodium carbonate yellow phosphorus Scenario 1 Scenario 2 Scenario 3 Fig. 4 CO 2 emissions of the six sub-sectors in the three scenarios in 2015 (million tons)

14 Scenario 1 Scenario 2 Scenario 3 Fig. 5 the total emissions of the six sub-sectors in the three scenarios in 2015 (million tons) The total CO 2 emissions in the six sub-sectors in the three scenarios are presented in Fig.5. As a whole, the six sub-sectors can offer 55.9 and million tons CO 2 reductions in Scenario 2 and 3, accounting for 12.0% and 26.8% of the baseline respectively. Compared to the emissions in 2007, if the technologies are not promoted, the total emissions amount will increase by 17.3% to million tons. Nevertheless a small extent of technological improvement in Scenario 2 will enable the emissions to stay at a stable level after 8 years development and a further improvement will result in 56 million tons or 14.1% reduction. 5. Policy implications and conclusions The CO 2 emissions in China s chemical industry were estimated through a two-level approach in this study. The calculations showed that at Level one, energy consumed by the entire industry resulted in 678 million tons CO 2 in 2007, contributing 11.3% to the nationwide total. Since 2000, the emissions grew at the high annual rate of 11.9%, making the control of CO 2 emissions in the industry of great urgency. Among tens of thousands of chemicals in this industry, coal-based ammonia, calcium carbide, caustic soda, coal-based methanol, sodium carbonate, and yellow phosphorus, which consumed the largest amounts of energy, were chosen as the six key sub-sectors for a detailed investigation in CO 2 emissions at Level two. The results showed that the six in total offered 58% CO 2 emissions of China s chemical industry in Key findings through this research include:

15 As the high emissions were primarily caused by coal dominance in fuel supply, reducing coal uses in chemical production technologies as well as power and heat generation technologies would offer significant reductions in this industry. The six key sub-sectors contributed the largest share to CO 2 emissions in the industry and thus have the highest priorities with regards to energy saving and CO 2 mitigation. The potential for decreasing carbon intensity vary tremendously among the six sub-sectors. In the most favorable scenario, the results vary between 21% and 42% compared to the 2007 baseline. This analysis presents a promising approach for China s chemical industry to control CO 2 emissions based on currently available technologies. Moreover, if other measures such as fuel switching are implemented at the same time, the reductions might be more significant. Nevertheless, the technological improvement is not easy to achieve without administrative intervention.. Acknowledgement The authors are grateful to Prof. Weiyang Fei from Tsinghua University and Prof. Weidong Zhang from Beijing University of Chemical Technology for their invaluable advices on this research work. This research is also financially supported by the projects of National Natural Science Foundation of China (NSFC), Ph.D. Programs Foundation of Ministry of Education of China and National Key R&D Program (No , No and No. 2009BAC65B03 respectively). References [1] Key World Energy Statistics. International Energy Agency, /keyworld2004.pdf; [2] CO 2 emissions from fuel combustion 2009 edition. International Energy Agency, Paris, France. [3] Cai WJ, Wang C, Wang K, Zhang Y, Chen J. Scenario analysis on CO 2 emissions reduction potential in China's electricity sector. Energy Policy 2007; 35:

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