Introduction to Coal Gasification CO₂ and Treatment Pathways
Coal gasification technology is a crucial method for the clean utilization of coal resources. The gasifier is the primary equipment for coal gasification, with various gasification methods available depending on coal properties and gas requirements.
I. Coal Gasification Process Overview
Gasifier → Low-Temperature Methanol Wash (Rectisol) → CO Shift → Synthesis Section
Low-Temperature Methanol Wash Process Flow:
- Coal Gasification: C+H₂O→CO+H₂+Impurities
(Adjusts CO/H₂ ratio)
2. CO Shift Reaction: CO+H₂O→CO₂+H₂
Two Absorption Methods:
- Two-Stage Absorption: For non-sulfur-resistant shift catalysts, desulfurize first (Rectisol), then shift CO, followed by CO₂ removal.
- One-Stage Absorption: For sulfur-resistant catalysts (more common currently).
II. Low-Temperature Methanol Wash (Rectisol) Technology
Developed by Linde & Lurgi (Germany, 1950s), Rectisol is a physical absorption method using methanol’s properties at -50°C to -60°C to remove CO₂, H₂S, and COS.
Advantages:
- High absorption capacity and purification efficiency
- Low solvent circulation due to high CO₂/H₂S solubility at low temps
- Selective regeneration (separate CO₂/H₂S recovery)
- A low methanol boiling point aids solvent regeneration.
- High specific heat minimizes temperature rise during absorption.
- Chemically inert, non-corrosive, and water-soluble (dries feed gas)
- Low viscosity reduces power consumption.
- Cost-effective and widely available
III. Analysis of VOC emissions from Low-Temperature Methanol Wash Sections under Different Gasification Processes
Through multiple communications with different gasification enterprises and testing of their low-temperature methanol wash exhaust gases, the VOC emissions from various gasifiers have been analyzed as follows:
(1) For fluidized bed gasification and entrained flow pressurized gasification, due to sufficient combustion, the VOC content in the exhaust gas from the low-temperature methanol wash section is very low. Therefore, these are not the focus of our study.
(2) For moving bed lump coal pressurized gasification, the exhaust gas from the low-temperature methanol wash section has high concentrations of combustible components and significant pollution, making it the primary focus of our study.
The non-methane total hydrocarbons (NMTHC) in the low-temperature methanol wash exhaust gas from gasifiers such as the Lurgi, Sedin, and BGL types exceed the standard limits severely and require treatment.
Given the high total amount of combustible components, adopting the RTO (Regenerative Thermal Oxidizer) process not only ensures compliant exhaust gas treatment but also generates a certain amount of steam as a byproduct, thus creating economic benefits.
IV.Selection of Vocs Treatment Process for Low-Temperature Methanol Wash Sections
The low-temperature methanol wash exhaust gas is characterized by a large volume, high concentration, and nearly zero oxygen content. It requires a substantial amount of fresh air or the introduction of VOC exhaust gases collected from the biological treatment tanks of the wastewater plant, loading/unloading areas, and tank areas for oxygen supplementation before being treated together, achieving comprehensive plant-wide VOC emission control.
