عنوان مقاله [English]
Ethylene dichloride unit is considered as one of the units with special importance in terms of the quality of wastewater. Chemicals 1,2-dichloroethaneor ethylene dichloride (EDC) are among the chemicals produced in the petrochemical industry. This material has major uses in industry including the production of polyvinyl chloride. As a product of the petrochemical industry, Ethylene D has dangerous environmental and health effects on animals and on the central nervous system (CNS) in humans. These effects include a decrease in information processing speed, flexibility, coordination speed and speech memory, and an adverse effect on visual ability .The wastewater of this unit contains 1,2-dichloroethane, water and FeCL3 particles. Due to the fact that the contents of the wastewater can affect the final efficiency of treatment in terms of COD concentration, taking remedial measures is essential for improving the situation within the design of the central treatment plant to control the existing situation. However, these methods are mostly at the end of the process and sometimes “costly” or there are no required resources to implement them. Therefore, it is essential to choose a method or a set of methods which can meet the current situation in terms of equipment, have compatible facilities and its operations can be controlled and have high reliability. In the present study, the factors affecting the amount of COD in the wastewater were investigated, along with the strategies to increase the efficiency of the wastewater treatment system by improving the performance of equipment and manpower with minimal economic costs.
In order to get acquainted with the production line, performance of equipment, and status of factory wastewaters based on design conditions, as well as determining the type of required tests, points and number of samples for analysis, and analyzing the documents related to the subject, the items were reviewed. Description of the plant process such as investigating the production line, performance of equipment, relation of processes, wastewater treatment system, operational parameters affecting the project Operational reports such as a review of changes in operational parameters such as pressure, temperature, flow, and concentration Operational plans such as checking the values of operational and environmental parameters in the design and normal condition of the factory Environmental reports such as a review of reported problems and main challenges Results of measurements such as checking the current status of wastewater outflows and inlets including COD, TSS, OIL, PH . Previous actions and research such as reviewing articles and reports related to the topic and using their results to help how to choose the path and avoid repetitive activities or special attention to important issues. In order to determine the characteristics and values of the parameters as well as evaluating the performance of equipment affecting the wastewater of the plant in real conditions, the items such as the efficiency of the treatment system by measuring COD and EDC in the inflow and outflow to the wastewater treatment system, the volume of wastewaters separately both in normal and emergency situations, and the performance of process by monitoring operational parameters such as temperature, concentration, and flow were considered for evalaution. Sampling was performed according to the sample analysis instructions of Kimia Petrochemical Company of Bandar Imam, number KM-WI-1001. First, the safety equipment including a cape, plastic gloves and glasses were worn and then a glass bottle with a capacity of 250 ml was prepared. For sampling from designated sites, the outlet valve of the sampling site was opened and let the remaining material leave the tube and fresh material to enter the tube after one minute. Then, the sampling bottle was rinced twice with the liquid inside the tube to remove any disturbing substances from the bottle. After filling the bottle with the desired material, the lid was closed tightly and was taken to the laboratory. A part of samples on which the necessary analyzes should be performed as grab samples were separated from the bottles and the analyzing operation was performed. The samples which should be considered as 24-hour composite samples were poured into a 2.5 liter glass container and stored in the refrigerator after closing the lid. Operational parameters were also read by measuring devices located in the control room and operating areas. In order to obtain the best result and increase the reliability, as well as the possibility of tracking and controlling the activities, planning was performed in such a way that two-hour samples were collected in different stages, and stored in a 24-hour composite and then analyzed. This process was repeated five days a week for each step. In this way, the performance of all shift groups was monitored and the operating conditions in a working week of the working day were evaluated. After reviewing the results, processing and analyzing the data, corrective solutions with the approach of improving processes and equipment as well as improving the efficiency of human resources were reviewed and presented.
The highest amount of increase in the efficiency of the treatment system in the outflow parameters of the treatment system is related to the flow rate of wastewater with a 25% increase and the lowest is related to the amount of EDC in the wastewater flow (3.3%). The highest efficiency of COD reduction in the inflow and outflow of wastewater to the treatment system was related to the third step of corrective actions with a reduction of 59%. The amount of COD in the outflow at the end of the project decreased by 54% compared to the beginning. The efficiency of the treatment system for this parameter was 16% compared to the beginning of the project. The highest efficiency of EDC reduction in the inflow and outflow of wastewater to the treatment system was related to the third step of corrective actions with a reduction of 93.5%. The amount of EDC in the outflow at the end of the project decreased by 33% compared to the beginning. The efficiency of the treatment system for this parameter was 3.3% compared to the beginning of the project. The highest efficiency of TSS reduction in the inflow and outflow of wastewater to the treatment system is related to the second step of corrective actions with 19.1% reduction. The amount of TSS in the outflow at the end of the project decreased by 23% compared to the beginning. The efficiency of the treatment system for this parameter was 7.6% compared to the beginning of the project. The efficiency of the treatment system for the flow rate of wastewater compared to the beginning of the project was 25%. Due to the fact that the wastewater of this plant has a small amount of OIL in the composition of the inflow to the treatment system, this parameter had no effect on the efficiency of the overall process. Since caustic soda is used to wash the product in the production process of this factory, and there is no function to control the pH in the neutral range in the treatment system, this parameter does not affect the overall process of wastewater treatment plant. In addition, due to the fact that EDC is absorbed from the outflow in the treatment process by transferring mass from the liquid phase (feed inlet to the treatment tower) to the gas phase (steam entering the treatment plant), adjusting the high and low temperature of the tower in the case of feed preheater converter is out of service is very important. Thus, adjusting the feed temperature at the moment of entering the treatment tower (about 85°C) must be done by steam injection to increase mass transfer (absorption of EDC from the liquid phase to the output gas phase of the tower).
Table 11 presents the factors with significant impact on the overall process of the wastewater treatment system, i.e. COD reduction
Based on the results of this study, the following suggestions should be considered to improve the process and achieve COD reduction. - Investigating the effect of using feed preheater converter on the efficiency of wastewater treatment system (not possible in this project) instead of steam entering the treatment tower. - Studying the reduction of TSS input to the treatment system by reducing this parameter by deposition in the settler and polyelectrolytes and its effect on the efficiency of the treatment system. Evaluating the reduction of flow rate of wastewater to the defined limit in the design documents by complete return of water in the third step of washing to the process cycle. Investigating an increase in the volume of wastewater treatment tower on EDC adsorption efficiency from feed flow using simulation software such as Hysis