Application of De-oiling and Coke Powder Removal Technology for Delayed Coking Sulfur-Bearing Wastewater in Refinery Wastewater Treatment
Given the unsatisfactory performance of existing de-oiling and coke powder removal technologies for coking sulfur-bearing wastewater, which easily leads to coking and plugging of downstream stripping units, SINOKLE has proposed a new chemical-free pretreatment process for coking sulfur-bearing wastewater. Centered on "cyclonic dissolved-air flotation + coalescing de-oiling", the process removes coke powder from the oil through coarse and fine filtration, then recovers high-quality light oil through an integrated coalescing de-oiler and cyclonic dissolved-air flotation unit, supplemented by filtration to remove coke powder.
CDFU unit principle
CDFU unit flow is shown in the figure. The unit mainly consists of an air suspension tank, a dissolved-air pump, a stabilization tank and corresponding control instruments. The principle of cyclonic dissolved-air flotation is as follows: a large number of highly dispersed micro-nano bubbles are first introduced into the wastewater to be treated; as carriers, these bubbles adhere to particles (oil droplets) or flocs suspended in the water, forming suspended bodies with an overall density lower than that of water, which rise to the surface under buoyancy to form floating oil, thereby completing solid-solid, solid-liquid and liquid-liquid separation.
Coalescing de-oiler unit principle
The coalescing de-oiler mainly consists of a flow stabilizer, modified coalescing fiber packing, oil collection pockets and corresponding control instruments; its structure is shown in the figure. Under the cyclonic centrifugal action at the inlet of the coalescing de-oiler, the sulfur-bearing wastewater undergoes a certain degree of coalescence; after flow stabilization by the stabilizer, the internal flow quickly becomes stable, and part of the waste oil is separated into the oil collection pocket. In the modified coalescing fiber packing zone, the emulsified oil is captured and coalesced into large oil droplets by the specially modified material, then detaches under fluid drag and enters the second oil collection pocket for recovery.
Figure. Structural principle of the coalescing de-oiler
(1) For coking sulfur-bearing wastewater in the non-small-purge stage, the combined process with "CDFU + coalescing de-oiling" as the core achieved an average outlet oil concentration of 175 mg/L against an average inlet oil concentration of 4,500 mg/L, an average de-oiling rate of 98.83%; with an average inlet suspended solids concentration of 353 mg/L, the outlet wastewater was clear and transparent with an average suspended solids concentration of 7 mg/L, demonstrating the excellent coke powder removal of this process.
(2) For coking sulfur-bearing wastewater in the small steam purge stage, the combined process with "CDFU + coalescing de-oiling" as the core achieved an average outlet oil concentration of 285 mg/L against an average inlet oil concentration of 197,000 mg/L, an average de-oiling rate of 99.85%; with an average inlet suspended solids concentration of 651 mg/L, the outlet suspended solids averaged 7 mg/L, showing the good resistance of this process to fluctuations.
(3) The combined coking sulfur-bearing wastewater treatment process centered on "cyclonic dissolved-air flotation + coalescing de-oiling" has the advantages of a small footprint and low operating cost, providing an industrially and economically practical technical reference for resource-oriented treatment of refinery oily wastewater.
Results from practical petrochemical project cases show that in the non-small-purge stage of delayed coking, the combined process achieved an average de-oiling efficiency of 98.83%; with an average inlet suspended solids concentration of 353 mg/L, the outlet suspended solids averaged 7 mg/L. In the small steam purge stage of delayed coking, both de-oiling efficiency and suspended solids removal improved to varying degrees.
Figure. High-emulsification acidic wastewater treatment project at a petrochemical company
This shows that the combined process delivers excellent de-oiling and coke powder removal for delayed coking sulfur-bearing wastewater and can provide a useful reference for the resource-oriented treatment of similar wastewater.
