Spent Caustic Treatment Using ClO2 Oxidation at Ambient Pressure
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Solution Overview
Problem
Conventional methods for treating spent caustic effluent, such as wet air oxidation (WAO), require high operating and capital expenditures due to extreme temperature and pressure conditions, and fail to completely remove residual hydrocarbons and sulfides, leading to inconsistent COD values and inefficiencies.
Innovation Solution
A system and method using chlorine dioxide solution for treating spent caustic effluent, involving alkali neutralization with mineral acid, temperature reduction, and mixing with ClO2 in cavitation or venturi equipment to oxidize sulfides and reduce COD, followed by biological treatment under normal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wet air oxidation is used to treat spent caustic effluent, then sulfide and COD are reduced, but high temperature and pressure conditions are required leading to high OPEX and CAPEX
Solution Approach 1:
The patent changes the operating parameters from high temperature and pressure (WAO conditions) to ambient temperature and pressure by using chlorine dioxide as the oxidizing agent. This parameter change maintains effective sulfide and COD reduction while eliminating the need for expensive high-pressure equipment and energy input
Solution Approach 2:
The patent employs chlorine dioxide, a strong oxidizing agent, to accelerate the oxidation of sulfides and organic matter in spent caustic effluent. This strong oxidation capability achieves complete sulfide removal and significant COD reduction without requiring the high energy input needed for conventional WAO processes
2Reliability
If wet air oxidation is used to treat spent caustic effluent, then sulfide and COD are reduced, but high temperature and pressure conditions are required leading to high CAPEX
Solution Approach 1:
The patent changes the operating parameters from high temperature and pressure (WAO conditions) to ambient temperature and pressure by using chlorine dioxide as the oxidizing agent. This parameter change maintains effective sulfide and COD reduction while eliminating the need for expensive high-pressure equipment and energy input
Solution Approach 2:
The patent replaces expensive, complex high-pressure oxidation equipment with a simpler system that uses chlorine dioxide solution as a consumable chemical oxidant. This substitution reduces capital expenditure by using a less expensive, easier-to-handle oxidizing agent that works under ambient conditions
3Quantity of substance
If wet air oxidation is used to treat spent caustic effluent, then partial COD reduction is achieved, but residual hydrocarbons and sulfides remain leading to inconsistent COD values
Solution Approach 1:
The patent employs chlorine dioxide, a strong oxidizing agent, to accelerate the oxidation of sulfides and organic matter in spent caustic effluent. This strong oxidation capability achieves complete sulfide removal and significant COD reduction without requiring the high energy input needed for conventional WAO processes
Solution Approach 2:
The patent performs preliminary oxidation of sulfides and organic matter using chlorine dioxide before the effluent enters the biological treatment system. This preliminary action ensures that refractory compounds are broken down into more biodegradable forms, leading to more consistent and complete COD removal in the subsequent biological treatment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Achieves complete sulfide and COD reduction with minimal chemical oxidant use and residence time, eliminating the need for high-pressure equipment, reducing capital and operating costs, and ensuring effluent suitability for biological treatment.
Implementation Method 1
adding ClO2 solution to the spent caustic solution to oxidize sulphide/thiols content for complete reduction of sulphide/mercaptane
Implementation Method 2
at least one of a cavitation (mixing) chamber or venturi mixing equipment mechanically connected downstream to the heat exchanger unit for adding ClO2 solution to the spent caustic solution
Implementation Method 3
a heat exchanger unit engaged with the acid storage container through a pipeline for reducing temperature of the neutralized spent caustic to 35-45° C.
Data Source
AI summary
The present invention generally relates to a system and method for treating spent caustic effluent using chlorine dioxide solution. The system comprises a spent caustic storage tank for receiving spent caustic obtained from refinery operations; an acid storage container connected to the spent caustic storage tank for neutralizing free alkali content with a mineral acid to eliminate unwanted chemical reactions associated with free caustic present in spent caustic with ClO2; a heat exchanger unit engaged for reducing temperature of spent caustic to 35-45° C. from high temperature raised due to heat of neutralisation at least one of a cavitation (mixing) chamber or venturi mixing equipment mechanically connected downstream of the heat exchanger unit for adding ClO2 solution to the spent caustic solution to oxidize sulphide/thiols content for complete reduction of sulphide/mercaptane and reduction of 80-90% of COD.