Melamine Offgas Scrubbing with Cooled Urea Melt Recirculation

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Solution Overview

Problem

The existing high-pressure melamine synthesis processes face issues with melamine cyanurate precipitation and corrosion in urea melt coolers due to the use of a double-stage scrubbing process, leading to operational inefficiencies and high investment costs.

Innovation Solution

A single-stage scrubbing process using urea melt to purify melamine offgas, with recirculated urea melt cooled to a temperature above 165°C and mixed with fresh urea melt, prevents melamine cyanurate precipitation and reduces corrosion, maintaining process efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a double-stage scrubbing process is used to purify melamine offgas, then the purification efficiency is improved, but melamine cyanurate precipitation and corrosion in urea melt coolers occur

Engineering Contradiction:

Improvepurification efficiencyVSAvoidoperational reliability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the temperature parameter of the recirculated urea melt by cooling it to a controlled temperature range before reintroduction. This parameter change prevents melamine cyanurate precipitation while maintaining purification efficiency, resolving the contradiction between purification performance and operational reliability.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If a double-stage scrubbing process is used to purify melamine offgas, then the purification efficiency is improved, but investment costs increase

Engineering Contradiction:

Improvepurification efficiencyVSAvoidinvestment cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent merges the purification stages into a single-stage scrubbing process where recirculated cooled urea melt is reintroduced. This consolidation maintains purification efficiency while reducing the number of equipment units and overall investment costs.

Inventive Principle:

Principle #5Merging (Combining)

3Loss of energy

If recirculated urea melt is cooled to recover heat, then energy efficiency is improved, but melamine cyanurate precipitation occurs

Engineering Contradiction:

Improveenergy efficiencyVSAvoidmelamine cyanurate precipitation

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent optimizes the cooling temperature parameter of the recirculated urea melt, maintaining it within a specific range that allows heat recovery while preventing melamine cyanurate precipitation. This controlled parameter change resolves the contradiction between energy efficiency and harmful precipitation.

Inventive Principle:

Principle #35Parameter changes

4Loss of energy

If the urea melt cooler operates at high efficiency, then heat recovery is improved, but corrosion risk increases

Engineering Contradiction:

Improveheat recovery efficiencyVSAvoidcorrosion

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent controls the temperature parameter of the recirculated urea melt to optimize the operating conditions of the urea melt cooler. By maintaining the temperature within a specific range, the system achieves efficient heat recovery while reducing corrosion risk through optimized thermal conditions.

Inventive Principle:

Principle #35Parameter changes

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

The single-stage process effectively purifies melamine offgas, reduces corrosion risks, and lowers equipment maintenance, while maintaining energy efficiency and reducing the risk of plant shutdowns.

Implementation Method 1

The contact between the offgas and the falling urea melt generates melamine precursors such as ammeline and cyanuric acid

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Implementation Method 2

The contact between the offgas and the falling urea melt generates melamine precursors

Methodology Applied

Scientific EffectChemical reaction: Chemical Bonding

Implementation Method 3

The recirculated portion of urea melt is cooled in a urea melt cooler prior to reintroduction into the first stage. Cooling the urea melt recovers the heat released by the scrubbing process

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 4

Cooling the urea melt recovers the heat released by the scrubbing process, particularly by the absorption of the offgas in the urea melt

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 5

said recirculated urea melt being cooled in a shell and tube heat exchanger

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Data Source

PatentUS20260062392A1Melamine process with purification of melamine offgas

Publication Date: 2026.03.05 CASALE SA

AI summary

A process for the synthesis of melamine including the purification of the offgas released by the synthesis of melamine by means of a single purification stage (6); in the purification stage (6), the offgas (3) is washed with fresh urea melt and with a recirculated urea melt (8) containing ammonia and melamine precursors (5); said recirculated urea melt is withdrawn from bottom of the single purification stage (6) and cooled in a shell and tube heat exchanger (11), optionally after mixing with the fresh urea melt (15), to a temperature of at least 165° C. preferably in the range 165° C. to 245° C. prior to reintroduction in the purification stage.