Exhaust Gas Recirculation Desulfurization via Flow Branching
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Solution Overview
Problem
Existing methods for desulfurizing exhaust gas recirculation in internal combustion engines face challenges such as high costs, complex process control, and corrosion issues with ammonia-based solutions, which limit effective desulfurization and nitrogen oxide reduction, especially when dealing with fuels of high sulfur content.
Innovation Solution
A method involving the targeted branching of exhaust gas flows to utilize ammonia for desulfurization, allowing for adjustable NH3 concentration in the exhaust gas recirculation system, using ammonia precursors like urea and catalysts to optimize desulfurization and nitrogen oxide reduction, and controlling the flow to prevent cooler blockage and optimize operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ammonia is used for desulfurization in the exhaust gas recirculation line, then desulfurization efficiency is improved, but ammonium sulfate precipitates block the cooler when temperature falls below 300°C
Solution Approach 1:
The exhaust gas flow is divided into two separate branches: one branch (first partial exhaust gas flow) is used for desulfurization by mixing with ammonia, while the other branch (second partial exhaust gas flow) bypasses the cooler and is mixed back later. This segmentation allows desulfurization to occur without the temperature drop that causes ammonium sulfate precipitation in a single-line system.
Solution Approach 2:
A bypass flow acts as an intermediary thermal mass that prevents the temperature of the desulfurization mixture from falling below the dew point of ammonium sulfate. The second partial exhaust gas flow that bypasses the cooler mixes with the desulfurized gas, maintaining temperature above 300°C and preventing precipitation while still allowing heat exchange in the cooler for the main flow.
2Reliability
If CaO or CaOH is added for desulfurization, then desulfurization is achieved, but heavy wear occurs on engine liners due to abrasiveness
Solution Approach 1:
The patent uses ammonia, a consumable reagent that reacts to form gaseous or easily removable ammonium sulfate, replacing durable but abrasive solid desulfurants like CaO. The ammonia is introduced in controlled amounts and consumed in the reaction, avoiding the mechanical wear problem while achieving desulfurization through chemical reaction.
3Reliability
If NH3 is used to reduce nitrogen oxides through SNCR, then nitrogen oxide reduction is achieved, but conversion is only 15-25% due to poor selectivity
Solution Approach 1:
The patent uses a catalyst as an intermediary substance to facilitate the SCR reaction between ammonia and nitrogen oxides. The catalyst enables the reaction to proceed with high selectivity and efficiency (over 95% conversion) at lower temperatures, replacing the non-catalytic SNCR process that suffers from poor selectivity and low conversion rates.
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 cost-effective and efficient desulfurization of exhaust gas recirculation, reducing nitrogen oxide emissions while minimizing corrosion and cooler blockage, allowing for independent optimization of desulfurization and nitrogen oxide reduction processes.
Implementation Method 1
2NH3 + SO3 + H2O --> (NH4)2SO4
Implementation Method 2
the exhaust gas must be reduced to temperatures below 300° C., advantageously to temperatures below 100° C.
Implementation Method 3
Urea, which releases NH3 in the hot exhaust gas, is usually used in vehicles instead of NH3. This decomposition can be improved by using a so-called hydrolysis catalyst
Implementation Method 4
there is the possibility of using NH3 to catalytically reduce nitrogen oxides downstream of the internal combustion engine through selective catalytic reduction (called the SCR method for short)
Implementation Method 5
2NH3 + 2NO + O2 --> 2N2 + 3H2O
Data Source
Figure 1~2
Figure 3
AI summary
A method and a device for desulfurizing an exhaust gas recirculation stream from an internal combustion engine are proposed. This recirculation stream is fed to the internal combustion engine (1) on its fresh air side (8), wherein ammonia is used for desulfurization in the exhaust gas recirculation stream (7"), and wherein at least one exhaust gas partial flow (7, 17) is diverted from the exhaust gas stream (2) of the internal combustion engine (1). According to the invention, it is proposed that at least one ammonia-releasing reactant (12) is fed to an exhaust gas partial flow (7) diverted from the exhaust gas stream (2) of the internal combustion engine (1), and that the exhaust gas partial flow (7') thus loaded is fed partly as exhaust gas recirculation (7") to the fresh air side (8) and partly as an aftertreatment partial flow (9) to an exhaust gas aftertreatment system.The amount of exhaust gas recirculation supplied to the fresh air side (8) and the amount of the aftertreatment partial flow supplied to the exhaust aftertreatment system (9) are specified and/or varied depending on at least one operating parameter defining the respective operating situation of the internal combustion engine (1) by means of a control and/or regulating device.