Urea Melamine Synthesis Loop Gas Splitting
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Solution Overview
Problem
Combined urea-melamine plants face reduced gaseous carbon dioxide availability in the reactor due to significant urea usage for melamine production, leading to lower conversion rates and increased energy consumption.
Innovation Solution
The process involves splitting the gaseous phase from the stripper into two portions, with one portion directly fed to the reaction section for heat balance and the other mixed with melamine off gas and recovered carbamate solution for condensation, ensuring efficient recycling and heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a significant amount of synthesized urea is used to produce melamine, then melamine production increases, but gaseous carbon dioxide availability to the reactor decreases
Solution Approach 1:
The invention changes the physical state parameter of carbon dioxide by introducing it as a supercritical fluid (temperature above critical temperature of 31.1°C and pressure above critical pressure of 73.8 bar) instead of gaseous state. This allows CO2 to be introduced in a condensed phase that can provide both the necessary quantity and the heat required for the endothermic carbamate dehydration reaction, thus resolving the contradiction between increased melamine production and reduced CO2 availability.
Solution Approach 2:
The invention uses supercritical CO2 as an intermediary substance that serves dual purposes: it acts as both the reactant (providing carbon dioxide) and the heat transfer medium (providing thermal energy). This intermediary approach allows the system to simultaneously address both the quantity deficit and the heat balance requirement, enabling increased melamine production without compromising reactor CO2 availability.
2Temperature
If gaseous carbon dioxide is condensed in the reactor, then heat balance is affected, but conversion rate decreases
Solution Approach 1:
The invention changes the physical state parameter of CO2 from gaseous to supercritical fluid phase. By introducing CO2 in supercritical state rather than gaseous state, the condensation process occurs differently, providing heat to the endothermic reaction without causing the adverse effects associated with gaseous CO2 condensation. This parameter change maintains both heat balance and conversion rate.
3Loss of substance
If melamine off gas is recycled to the urea reactor, then reagent utilization improves, but reactor cooling occurs
Solution Approach 1:
The invention changes the thermal state of the recycled CO2 by introducing it in supercritical form with elevated temperature and pressure. This supercritical CO2 serves as a hot stream that provides heat to the endothermic carbamate dehydration reaction, thereby compensating for the cooling effect that would otherwise occur when recycling melamine off gas. This resolves the contradiction between improved reagent utilization and maintained reactor temperature.
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 enhances the recycling efficiency of melamine off gas, maintains reactor temperature, reduces energy consumption, and minimizes inert gas presence, thereby improving the overall synthesis process efficiency and reducing equipment size requirements.
Implementation Method 1
a condensation section, configured to condense a portion of the gaseous phase emerging from the stripping section
Implementation Method 2
the reaction of carbon dioxide with ammonia (forming the ammonium carbamate) is exothermic and generates the heat required by the endothermic dehydration of carbamate
Implementation Method 3
the reaction of carbon dioxide with ammonia (forming the ammonium carbamate) is exothermic and generates the heat required by the endothermic dehydration of carbamate
Data Source
Figure 1
Figure 2
AI summary
An integrated process for the synthesis of urea and melamine, wherein: urea is synthesized with a stripping process in a high-pressure synthesis loop comprising a reactor, a stripper and a carbamate condenser, and the urea solution leaving said stripper is sent to a recovery section to produce a concentrated urea product and a recovered carbamate solution; at least part of said urea product is converted to melamine, and the off-gas from the synthesis of melamine are recycled to the urea synthesis by mixing with the gas phase from the stripper and with said recovered carbamate solution, thus forming a mixed flow which is then condensed in said carbamate condenser, and the condensate is eventually directed to the reactor.