Research On Water-Energy-Environmental Pollutant Nexus And Evaluation Method For Cleaner Production Technology In Petrochemical Industry

The petrochemical industry is a typical high-consumption and high-pollution industry.Water saving,energy saving,and pollutant reduction are the key goals of the petrochemical industry.Therefore,it is very important to identify the improvement potential and implement cleaner production technology in this industry.There exists significant coupling among water consumption,energy consumption and the generation of pollutants in the petrochemical production process.Therefore,the conventional method of individually evaluating the indicators of water saving,energy saving,and pollutant reduction cannot accurately identify the improvement potential and screen out the optimal technology.There is a lack of comprehensive evaluation methods to identify the potential for water saving,energy saving,and pollutant reduction,and then guide the selection and implementation of the optimal cleaner production technology based on the coupling relationship and the overall perspective of water–energy–environmental pollutants nexus（WEEN）.This research is carried out from two aspects:integrated analysis of coupling relationship,and evaluation and screening of cleaner production technology.Taking a typical petrochemical enterprise in China as a case,this research identified the potential for water saving,energy saving,and pollutant reduction,formulated improvement strategies,and selected the best cleaner production technology.The main content and results of the paper are as follows:（1）A“3M”integrated analysis method was established to identify and quantify the WEEN coupling relationship of petrochemical enterprises.“3M”refers to a generic petrochemical WEEN model,material and energy flow analysis,and a WEEN analysis matrix.Three quantitative indicators based on the“3M”method were established,including WEEN-related percentage,coupling relationship number pairs,and WEEN correlation intensity.The coupling relationship was quantified and analyzed at the system,element,and unit levels.The case study shows that at the system level,95.87%of water consumption,61.97%of energy consumption,and 54.99%of pollutant generation are coupled.The energy subsystem is dominant in WEEN and it is the root of high consumption and pollution.At the element level,based on synergies and trade-offs,the 9 elements are divided into 3optimization priorities,namely high priority（deoxidized water and fuel）,medium priority（steam,circulating water,and wastewater）,and low priority（fresh water,demineralized water,waste gas,and electricity）.At the unit level,the 10 units are divided into 3 levels according to their potential of overall water saving,energy saving,and pollutant reduction.Based on the coupling relationship,the improvement strategies were formulated.Compared with the conventional method overlooking the coupling relationship,it was found that the conventional method has overestimated potential（hydrotreating units and delayed coking units）and underestimated potential（atmospheric and vacuum distillation unit）.（2）An evaluation method for cleaner production technology in the petrochemical industry based on coupling relationship was constructed.The method includes constructing an analytical framework,using material and energy flow analysis to quantify the coupling relationships and calculate the direct and indirect water saving,energy saving,and pollutant reduction of technologies,and using the established environmental and economic benefit indicators to screen the optimal cleaner production technology.A list of 37 cleaner production technologies for the petrochemical industry was established based on the recommended technologies issued by China and the European Union.For the case enterprise,a total of 11optimal cleaner production technologies distributed in 7 cost ranges were selected.The technology with the best comprehensive benefits can save 8.95 million tons of water and 27000 tons of energy,reduce emissions of 354 400 tons of waste gas and 326 700 tons of wastewater per year,the emissions of SO₂,NO_x,dust,COD and ammonia nitrogen can be reduced by 4.47,12.57,2.41,16.66,and 0.19 t,respectively,and the environmental benefit is0.62.The operating cost can be saved by 120 million yuan per year,and the economic benefit（benefit-cost ratio）is 1.41 a^-1.