Roasting Plant Gas Recirculation for Energy Savings
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Solution Overview
Problem
Existing roasting plants face challenges in achieving complete oxidation of roasting gases at temperatures below 800°C, leading to inefficient energy use and the need for costly purification systems to comply with ecological norms, as they operate at temperatures between 300°C and 500°C, resulting in the discharge of non-perfectly oxidized gases into the atmosphere.
Innovation Solution
A roasting plant design that incorporates a post-combustion heat-exchanger to reach temperatures above 760-820°C for almost-total elimination of total organic carbon, allowing the roasting temperature to be maintained within the necessary range of 300-500°C, with discharge gases being partially recycled to the combustion chamber for energy efficiency and auto-burning due to heat developed by gas oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If roasting is performed at temperatures between 300°C and 500°C, then the product is not damaged and roasting quality is maintained, but the discharge gases are not completely oxidized and require costly purification systems
Solution Approach 1:
The system separates the roasting process from the oxidation process. Roasting occurs at 300-500°C in the roasting chamber while oxidation of discharge gases occurs at higher temperatures in a separate oxidation chamber, allowing both requirements to be met simultaneously
Solution Approach 2:
A heat exchanger is introduced as an intermediary device that transfers heat from the hot oxidation gases to the incoming air and roasting gases, enabling the oxidation process to occur at higher temperatures while the roasting process maintains its required temperature range
2Object-generated harmful factors
If roasting gases are heated to 800°C for complete oxidation, then ecological standards are met, but the product is irremediably damaged and excessive energy is consumed
Solution Approach 1:
The system divides the thermal processing into two separate pathways: roasting gases are oxidized at high temperature (800°C) in the oxidation chamber while the product remains in the roasting chamber at controlled temperatures (300-500°C), preventing product damage while achieving complete oxidation
Solution Approach 2:
The heat exchanger acts as an intermediary that allows heat transfer from the oxidation process to the roasting process, enabling the oxidation chamber to reach 800°C for complete oxidation while the roasting chamber maintains temperatures suitable for product quality
3Object-generated harmful factors
If purifying plants are installed to oxidize toxic substances in discharge gases, then ecological compliance is achieved, but installation and management costs increase significantly
Solution Approach 1:
The oxidation function is merged with the existing combustion chamber and flue gas pathway. The combustion chamber serves dual purposes: generating heat for roasting and oxidizing discharge gases, eliminating the need for separate purifying plants
Solution Approach 2:
The combustion chamber is designed to perform multiple functions: heating air for roasting, oxidizing discharge gases to meet ecological standards, and providing heat through heat exchange. This multi-functionality eliminates the need for dedicated purification equipment
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 solution enables significant energy recycling and heat savings, reducing the specific energy consumption by 48% compared to traditional systems, while ensuring compliance with ecological standards by effectively eliminating total organic carbon emissions.
Implementation Method 1
the discharge gas is subjected to an oxidising process before it is issued into the atmosphere... a post-combustion heat-exchanger internally of which the gases reach temperatures of above 760-820°C, which temperatures guarantee an almost-total elimination of the total organic carbon, enabling the roasting temperature to be kept to the strictly necessary values
Implementation Method 2
The discharge gas treatment process in the post-combustor is a substantially-exothermic oxidising process, and only requires ignition in order to auto-burn due to the heat developed by gas oxidation
Implementation Method 3
A roasting plant design that incorporates a post-combustion heat-exchanger... enabling significant energy recycling and heat savings, reducing the specific energy consumption by 48% compared to traditional systems
Implementation Method 4
The gases, known as roasting gases, pass through the roasting chamber and are directly discharged into the atmosphere through a chimney, after first passing through a cyclone device to separate the solid particles
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A roasting plant for coffee, barley, cocoa and oil seed, generally comprising a roasting chamber (1) destined to contain a product to be roasted, a first combustion chamber (2) comprising a first burner (3) for generating and conveying a roasting gas flow into the roasting chamber (1); means for removing (4) from the roasting chamber discharge gases comprising the roasting gases and gases emitted by the product during roasting; means for reducing (6) organic components present in the discharge gas, and means for conveying (7) the discharge gas into an outside atmosphere, in which between the means for reducing the organic components present in the discharge gas and the means for conveying (7) the discharge gases into the atmosphere there is a branch (12) which conveys a part of the discharge gases from the means or reducing (6) the organic components into the roasting chamber (1).