Oxidant Injection Device for Underground Coal Gasification
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Solution Overview
Problem
Current underground coal gasification processes face challenges in achieving continuous oxidant injection, safe use of high oxygen concentrations, and efficient control of combustion and gasification, leading to fluctuations in product gas quality and operational inefficiencies.
Innovation Solution
An oxidant injection device with a swivel joint, coiled tubing, and mechanical shear-off device allows for continuous injection of high oxygen concentration oxidants, enabling flexible retraction and stable operation by using the annulus between the coiled tubing and injection well liner as a coolant flow path, reducing retraction time and distance, and employing temperature, pressure, and acoustic sensors for process control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high oxygen concentration oxidant is used to improve syngas calorific value, then product gas quality is improved, but combustion zone temperature increases causing high burn-back rate and damage to injection well liner
Solution Approach 1:
A coolant injection system is introduced as an intermediary between the high oxygen concentration oxidant injection and the combustion zone. The coolant (water or steam) is injected into the combustion zone to absorb excess heat and control the temperature, thereby enabling the use of high oxygen concentration oxidant without causing excessive temperature rise that would lead to high burn-back rate and damage to the injection well liner.
2Adaptability or versatility
If oxidant injection is stopped during retraction to move injection position, then injection well system can be repositioned, but continuous gasification operation is interrupted causing product gas quality fluctuations
Solution Approach 1:
The system maintains continuous oxidant injection during the retraction process by using a retractable oxidant injection device that can be pulled back through the injection well while continuing to inject oxidant. This allows the combustion zone to be repositioned without interrupting the gasification operation, thereby maintaining continuous product gas production and avoiding quality fluctuations.
3Ease of operation
If oxidant nozzle is sheared off during retraction to enable coiled tubing retrieval, then coiled tubing can be pulled back to surface, but oxidant injection continuity may be affected
Solution Approach 1:
The oxidant injection device is segmented into two main parts: the oxidant nozzle that remains in the combustion zone and the coiled tubing that can be retrieved to the surface. A mechanical shear-off device is provided that can shear the oxidant nozzle from the coiled tubing if the nozzle becomes stuck during retraction. This segmentation allows the coiled tubing to be retrieved while maintaining oxidant injection continuity through the remaining in-situ nozzle.
Data Source
AI summary
An oxidant injection device for an underground coal gasification process includes an oxidant pathway which includes a swivel joint, coiled tubing, and a mechanical shear-off device which are in gas tight connection with each other in that sequence. Attached to the mechanical shear-off device is an oxidant nozzle, wherein the shear-off device is adapted to shear the oxidant nozzle to allow retraction of the coiled tubing when necessary, and wherein the swivel joint causes the surface oxidant source to be in gas tight connection with the coiled tubing reel center shaft, thereby allowing continuous oxidant injection during the process of moving the oxidant nozzle via the movement of the coiled tubing when rotating the coiled tubing reel.