Parallel Methanation Reactors for SNG Production
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Solution Overview
Problem
Existing SNG production processes require high gas recirculation rates to control exothermal reactions, leading to large and expensive compressors, increased reactor sizes, and higher costs, making the process less competitive with fossil natural gas.
Innovation Solution
Feeding fresh syngas in parallel to multiple reactors with reduced recirculation, where each reactor receives a portion of the fresh syngas and partially converted gas, and using steam addition to control reaction temperatures and equilibrium, thereby reducing the need for extensive gas recirculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high gas recirculation rates are used to control exothermal reactions, then reaction temperature is controlled, but compressor size and cost increase significantly
Solution Approach 1:
The invention divides the single methanation reactor into multiple series-connected reactors (typically 3-5 reactors). Each reactor handles a portion of the conversion, distributing the exothermal heat generation across multiple units. This segmentation allows better temperature control with reduced recirculation ratios, as each reactor operates at lower conversion per pass, reducing the need for excessive dilution with recirculated gas.
Solution Approach 2:
The invention introduces inter-cooling stages between the series-connected reactors as intermediary heat removal mechanisms. Instead of relying solely on gas recirculation for heat control, heat exchangers are placed between reactors to remove excess heat at intermediate stages. This intermediary approach allows temperature control without requiring the same level of gas recirculation, reducing compressor power requirements.
2Temperature
If high gas recirculation rates are used to control exothermal reactions, then reaction temperature is controlled, but reactor size and catalyst quantity increase
Solution Approach 1:
By segmenting the methanation process into multiple series reactors, each reactor operates at a lower conversion level per pass. This allows smaller reactor volumes and less catalyst per unit while achieving the same overall conversion. The segmentation distributes the thermal load and allows more efficient use of catalyst bed volume across multiple smaller units rather than one large reactor requiring excessive recirculation.
3Temperature
If high gas recirculation rates are used to control exothermal reactions, then reaction temperature is controlled, but production cost increases
Solution Approach 1:
The multi-reactor segmented configuration reduces the overall recirculation ratio required for temperature control, directly reducing compressor power consumption and operational costs. While the number of reactors increases, the reduced catalyst quantity per reactor and lower energy consumption result in overall cost reduction, making SNG production more competitive with fossil natural gas.
Solution Approach 2:
The inter-cooling heat exchangers serve as intermediary heat removal devices that reduce the thermal load on the recirculation system. By removing heat at intermediate stages, the system requires less recirculation for temperature control, reducing compressor energy consumption and operational costs while maintaining safe operating temperatures.
4Speed
If high gas recirculation rates are used to control exothermal reactions, then reaction rate is controlled, but flow rate through reactors increases
Solution Approach 1:
By dividing the conversion into multiple series reactors, each reactor operates at a more moderate flow rate with lower conversion per pass. This segmentation allows better control of reaction kinetics without requiring excessive recirculation to dilute the fresh syngas, thus maintaining productivity while controlling the reaction rate through distributed conversion rather than high recirculation dilution.
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 results in a smaller, less expensive compressor and reduced catalyst requirements, lowering operational costs while maintaining effective heat recovery, making SNG production more competitive with fossil fuels.
Implementation Method 1
the above reactions are carried out in a so-called methanation section comprising a plurality of adiabatic reactors with heat recovery and gas recirculation. The reactors contain an appropriate catalyst to increase the yield of the reaction
Implementation Method 2
Basically, the process of methanation of the syngas involves the following, strongly exothermal reactions: (I) CO+3 H2 → CH4 + H2O (II) CO2 + 4 H2 → CH4 + 2 H2O where reaction (I) has a thermal output (enthalpy of reaction) of around 206 kJ/mol and reaction (II) of around 165 kJ/mol
Implementation Method 3
heat recovery is provided by heat exchangers cooling the hot gas stream at the outlet of each reactor e.g. by producing high pressure steam
Implementation Method 4
heat recovery is provided by heat exchangers cooling the hot gas stream at the outlet of each reactor e.g. by producing high pressure steam
Implementation Method 5
The gas recirculation requires the provision of an appropriate compressor
Implementation Method 6
The reactors contain an appropriate catalyst to increase the yield of the reaction
Data Source
Figure 1
AI summary
A process for producing substitute natural gas (SNG) comprising the steps of reacting a fresh syngas (11) into a methanation section (10) comprising adiabatic reactors (101-104) connected in series, with heat removal and reacted gas-recirculation, wherein the fresh syngas is fed in parallel to said adiabatic reactors. In a preferred embodiment the reacted gas is recirculated to the first reactor (101) and further dilution of the fresh gas at the inlet of the first and second reactor is achieved by steam addition.