What Is Oxy-Fuel?

Oxy-fuel combustion is a new type of combustion technology. Its basic principle is to separate the oxygen in the air as an oxidant and send it to the furnace for combustion with circulating flue gas. The main component of circulating flue gas is CO2, Therefore, the gas in the furnace is mainly O2 and CO2 gas, which is different from the N2-based combustion atmosphere in the furnace during traditional air combustion. The exhaust CO2 concentration at the tail of the boiler is very high, up to 95%, which facilitates the direct capture of CO2, and is a very promising technology for controlling greenhouse gas emissions.

Chinese name: Oxyfuel combustion

Foreign name: oxy-fuel combustion

Introduction to oxyfuel combustion

Basic principles of oxyfuel combustion Excluding the high concentration of CO2 in the flue gas, which can reach 95% to facilitate the direct capture of CO2, is a very promising technology for controlling greenhouse gas emissions.

Oxyfuel combustion research unit

The research on oxyfuel combustion technology at home and abroad has been carried out for many years, and some progress has been made. The technologically advanced countries such as the United States have established oxyfuel combustion demonstration power stations, and domestic research has also been carried out for many years. Among them, Southeast University, Huazhong University of Science and Technology, Tsinghua University, and Xi'an Jiaotong University are leading the research in this field. Among them, Southeast University's research in this area is relatively systematic and has established a small industrial model. The research has achieved a number of results over the years.

The difference between oxyfuel combustion and traditional air combustion

1. In order to obtain a similar adiabatic flame temperature, the oxygen concentration in the burner is relatively high. Under about 60% of the flue gas cycle, the input oxygen concentration is about 30%, which is much higher than 21% under air conditions.

2. The high concentration of carbon dioxide and water vapor in the boiler leads to higher gas radiance. When the oxygen concentration in the burner is less than 30%, the similar radiant heat transfer occurs in the boiler in the oxygen / fuel combustion.

3. After the flue gas is recirculated, the gas flow through the boiler is reduced by 80%.

4.Because the molecular weight of carbon dioxide is 44 and nitrogen is only 28, the density of the flue gas has increased.

5. The circulating flue gas is divided into dry cycle and wet cycle. If the water vapor in the cycle is not removed and the cycle is directly circulated, the candle-like sulfur-containing gas will have a higher concentration than that in the air combustion mode.

4 Oxy-fuel combustion 4 equipment

(ASU) Oxyfuel combustion air separation unit (ASU)

When improving the existing pulverized coal power plant, the first thing to do is to use air separation equipment to separate the oxygen required for combustion. At present, the air separation technology that can meet the required volume and purity is based on low-temperature steaming halls. The air is compressed, cooled and cleaned and then introduced into the steam feed tower to separate it into an oxygen-rich stream and a nitrogen-rich stream. Low temperature air separation is a high energy consuming technology. If you want to reach 95% oxygen concentration, you need to consume 0.24kWh / kg of energy. Although the oxyfuel combustion technology requires an air purity of 85% -98%, which is lower than the industrial demand of 99.5% -99.6%, these low-temperature steaming hall processes consume more than 15% of the total power output.

(CPU) Oxygen fuel combustion carbon dioxide purification equipment (CPU)

Carbon dioxide purification equipment includes gas cleaning equipment, including removal of moisture, particulate matter, and other pollutants in the flue gas. Oxyfuel combustion technology is very suitable for retrofitting.The traditional catalytic combustion (SCR), electrostatic precipitator (ESP), and flue gas desulfurization (FGD) equipment in traditional air combustion equipment can continue to be used to remove nitrogen oxides , SOx in particulate matter and flue. These pollutant control devices are also suitable for use in combination with amine capture after combustion. Impurities that cannot be condensed, such as oxygen, may cause gas candle damage and rotten candles during transportation, which will greatly affect the safety of carbon dioxide storage. Therefore, in addition to removing acid gases such as SOx and NOx, the non-condensable gases N ₂ and O ₂ should also be purified. So this part must include a multi-stage compression unit with inter-stage cooling to separate the inert gas.

(FGR Oxyfuel-fired flue gas recirculation system (FGR)

Recycled flue gas is used to replace nitrogen and adjust the combustion temperature. Considering the overall system efficiency and operational feasibility, the flue gas can be divided into two types, dry and wet, to circulate at different positions at the end of the economizer. In the early days of researching oxygen / fuel combustion technology, the purity of carbon dioxide was not the most concerned, and desulfurization and desulfurization equipment was not considered necessary. Therefore, all the smoke comes from the ESP in dry and wet form. Later, Dillon et al. Suggested that the primary stream of flue gas is circulated at different locations to transport pulverized coal, and the secondary stream of flue gas is used to improve energy efficiency. The primary stream of flue gas must be dried and reheated to 250-300 ° C to remove moisture from the pulverized coal. The secondary stream is used to circulate at higher temperatures. Drying is not required to remove the cooling and reheating Thermodynamic loss. Now, due to the requirements of pipeline transportation and storage, carbon dioxide concentration has become more demanding. Due to the multiple cycles of the flue gas, the concentration of sulfur dioxide will be 2 to 3 times higher than that of the traditional air combustion method. Therefore, for medium sulfur coal or high sulfur coal, the flue gas primary stream must be at least partially desulfurized to avoid coal grinding. Candle in the machine and smoke duct.

Oxyfuel combustion pressurization system

This has been proposed in recent years with the goal of improving energy efficiency by compensating for potential thermal energy in the flue gas. Increasing pressure reduces the volume of the flue gas, which promotes smaller devices and reduces capital costs at the same output power. Many studies have also reported the technical and economic feasibility of this aspect, and believe that increased pressure can improve overall efficiency. ^[1]