Font Size: a A A

Retrofit, Operation And Control Of 80t/hr Coal-gasification Wastewater Treatment Installation

Posted on:2010-11-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:D C FengFull Text:PDF
GTID:1101360302973773Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Because of the deficiencies in the current coal gasification wastewater treatment process, the phenol concentration in treated wastewater is excessively high and the treated wastewater can not meet the standards for discharged. To solve these severe problems, improve the performance of the treatment process and pursue clean production, in this dissertation, a typical coal-gasification wastewater treatment process is analyzed, modeled, simulated to identify bottlenecks of the process, and then a new scheme is proposed and implemented, so that treated wastewater can meet the subsequent biological treatment process.An effective thermodynamic model for the wastewater is established on the analysis, simplification and calculations, and some important units in process are analyzed and simulated with it. The results show that the existing process exist following problems: (1) the pH value of the current extraction system to the range of 9 to 10.5, which leads to a poor performance of phenol removal; (2) process de-acid efficiency is low, some salts can produced easily that make the pipeline obstructed; (3)with a greater losses of the extracting solvent DIPE.A single-stripper technology used in refining industry for the removal of hydrogen sulfide and ammonia in wastewater is simulated, and then this technology is introduced to the retrofit of current coal-gasification wastewater process. Two key improvements are made in the new process. First, the carbon dioxide and ammonia were removed simultaneously in a single striper where sour gas (mainly carbon dioxide) is removed from the tower top, the ammonia vapor is drawn from the side and recovered by partially condensation. Second, the ammonia is removed before the phenol recovery to reduce the pH value of the subsequent extraction units, so as the phenol removal permanence of the extraction is greatly improved. To ensure the operational efficiency, some key operational parameters are analyzed and optimized though simulation.The dynamic model of stripper is established, and then the dynamic performances to the disturbances such as feed composition, flow rate etc, are analyzed. Therefore, the rational control scheme is determined to the stripper of new process. The implementation of process control including setting of the control points, sampling, DCS systems, the computer system and configuration, PID parameter tuning, etc. has also been discussed in this paper. The industrial results show that the control scheme is reasonable and the system is running stable and easy to operate. A soft sensor of the NH3 concentration in bottom is established based on real-time data and partial least squares regression model, in which the major operating parameters are independent variables. Relative to multiple regression models, partial least squares model can effectively overcome the problem of correlation among operational parameters. The simulation results show that the predicting correctness and efficient of the soft sensor established is desirable. The proposed model suffices for the requirements of control and optimization for processes.The new process is implemented successfully in the industry and operated stably. Real industrial application demonstrates attractiveness of the new technique: it removes above 99% CO2, compared to known techniques remove about 60%, and the ammonia is also effectively removed. As a result, the pH value of wastewater is reduced to below 7. It ensures that the phenol removal ratio of modified process increased above 30% than that of old process in the following extraction units. In consequence, the biochemical treatment of wastewater becomes easier.The successful industrial implementation made an attractive case to treat the troublesome coal-gasification waste water.
Keywords/Search Tags:Coal-gasification wastewater, Phenol, Flowsheeting simulation, Control, Soft sensing
PDF Full Text Request
Related items