Solid Fuel Gasification with Segmented CaO Reactors
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Solution Overview
Problem
Existing gasification methods face challenges in achieving high efficiency and purity of hydrogen production due to the incompatibility of CaO's catalytic function for tar reforming and CO2 absorption, requiring high temperatures and pressures, which are costly and restrict application to low-capacity systems.
Innovation Solution
A method dividing the gasification process into three phases: pyrolysis gasification, char combustion, and gasified gas purification, where inactive chemicals are calcined to generate active CaO, which absorbs CO2 at low-medium temperatures and reforms tar at high temperatures, allowing for independent control of reaction temperatures to optimize both processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If CaO is used to absorb CO2 in gasified gas at high temperature (1123K or more), then the gasification reaction speed is sufficient, but CO2 absorption is restricted by chemical equilibrium and requires high pressure (20 atm or more)
Solution Approach 1:
The gasification process is divided into two separate reactors: a gasification reactor operating at low/medium temperature (773-1073K) where CO2 is absorbed by CaO, and a combustion reactor operating at high temperature (1073K or more) where CaCO3 is decomposed to regenerate active CaO. This segmentation allows each reactor to operate under optimal conditions without the conflicting requirements of high temperature and high pressure simultaneously.
Solution Approach 2:
Active CaO is prepared in advance in the combustion reactor by decomposing CaCO3 at high temperature, then this pre-prepared active CaO is transferred to the gasification reactor where it absorbs CO2 at low/medium temperature. This preliminary preparation of the chemical absorbent allows the CO2 absorption process to proceed efficiently at lower pressures.
2Object-generated harmful factors
If CaO is used as catalyst for tar reforming, then tar is removed from gasified gas, but this requires high temperature (1123K or more) which conflicts with the low/medium temperature needed for CO2 absorption
Solution Approach 1:
The gasification process is divided into two separate reactors: a gasification reactor operating at low/medium temperature (773-1073K) where CO2 is absorbed by CaO, and a combustion reactor operating at high temperature (1073K or more) where CaCO3 is decomposed to regenerate active CaO. This segmentation allows each reactor to operate under optimal conditions without the conflicting requirements of high temperature and high pressure simultaneously.
Solution Approach 2:
CaCO3 serves as an intermediary carrier that transports thermal energy from the high-temperature combustion reactor to the low/medium-temperature gasification reactor. The decomposition of CaCO3 in the combustion reactor and its subsequent reaction with CO2 in the gasification reactor facilitates heat transfer while enabling tar reforming and CO2 absorption in separate temperature zones.
3Use of energy by stationary object
If solid fuel is burned for combustion to provide heat, then sufficient heat supply is achieved, but inert gases (CO2 and N2) are admixed in the gasified gas, lowering purity and heat quantity
Solution Approach 1:
The system is divided into separate gasification and combustion reactors. The gasification reactor produces hydrogen-rich gas without direct combustion of the fuel, while the combustion reactor burns char to generate heat. This separation prevents inert gases from combustion from contaminating the product gas, maintaining high purity while still providing sufficient heat supply.
Solution Approach 2:
The harmful combustion process is extracted from the gasification reactor and placed in a separate combustion reactor. Only the beneficial heat supply function remains in the gasification reactor, while the combustion products (inert gases) are isolated in the separate combustion reactor, thus preserving the purity of the gasified product.
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
This approach enables high-efficiency gasification at normal pressure with unified gas purification, producing high-quality hydrogen by ensuring compatible functions for CO2 absorption and tar reforming, reducing tar and impurities in the gasified product.
Implementation Method 1
CO2 in gasified gas generated by pyrolysis and gasification of the solid fuel is absorbed by the active chemical at a low or medium temperature
Implementation Method 2
tar in the gasified gas is reformed with the active chemical functioning as catalyst at a high reaction temperature
Implementation Method 3
tar in the gasified gas generated by the pyrolysis and gasification of the solid fuel is reformed in the gasified gas purification phase at the high reaction temperature in said phase
Implementation Method 4
heat fluid medium being circulated between these gasification and combustion furnaces to transfer heat from the combustion furnace to the gasification furnace
Implementation Method 5
the low-active chemical less-activated through reaction with said CO2 and newly added inactive chemical, said char being burned by an oxidizing agent to bring about combustion heat with which said low-temperatured heat medium is heated and said low-active and inactive chemicals are calcined to be re-activated and activated, respectively
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A function of absorbing CO2 in gas by chemical to accelerate gasifying reaction is made compatible with a catalytic function of reforming tar in gasified gas generated by the gasifying reaction to thereby make it possible to produce clean product gas with high gasification efficiency. Gasification process is divided into three processes: a gasification furnace 10 for carrying out gasification process by pyrolysis and gasification (pyrolysis gasification phase, first process), a combustion furnace 20 for burning char to obtain calcined active chemical (char combustion phase, second process) and a gas purification furnace 30 for purifying gasified gas (gasified gas purification phase, third process). Through heat transmission by fluid heat medium and chemical and through harmony of chemical reactions in respective phases by the chemical, the gasification furnace 10 is independently controlled to a low or medium temperature (773-1073°K) which is required for gasification and which enables absorption of CO2; and the gas purification furnace 30 is controlled to a high temperature (1073°K or more) required for gas purification.