Combustion system and method for heating process air for paper drying systems
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Solution Overview
Problem
Current paper drying systems for toilet paper face inefficiencies due to excessive heat loss, incomplete combustion, and high nitrogen oxide emissions, primarily caused by the overuse of atmospheric combustion air and the semi-open nature of the drying process.
Innovation Solution
A combustion system that utilizes both conventional and alternative fuels, recycles process air to reduce atmospheric combustion air usage, and employs a dual-fuel burner with a specially designed combustion chamber to ensure complete oxidation and minimize pollutant emissions, allowing for controlled temperature adjustment and reduced heat losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If atmospheric combustion air is used in excess of stoichiometric ratio to control flame temperature, then nitrogen oxide emissions increase, but combustion completeness improves
Solution Approach 1:
The patent changes the composition parameter of the combustion air by replacing a portion of atmospheric air with recycled process air that has been enriched with oxygen through contact with the steam-heated cylinder surface. This parameter change allows maintaining complete combustion while reducing nitrogen oxide emissions by limiting the amount of atmospheric air introduced.
Solution Approach 2:
The steam-heated cylinder surface acts as an intermediary device that transfers oxygen from the pressurized steam inside the cylinder to the combustion air outside. This intermediary mechanism provides a controlled source of oxygen that replaces the need for excess atmospheric air, thereby reducing nitrogen oxide formation while ensuring complete combustion.
2Loss of energy
If combustion air is heated in air/air heat exchangers, then energy efficiency improves, but the system complexity increases
Solution Approach 1:
The steam-heated cylinder serves multiple functions simultaneously: it dries the paper sheet through steam heating, and it preheats the combustion air through oxygen transfer and thermal contact. This multi-functionality eliminates the need for separate air/air heat exchangers, reducing system complexity while maintaining energy efficiency.
Solution Approach 2:
The patent merges the steam heating function and the combustion air preheating function into a single integrated system. The steam-heated cylinder both dries the paper and prepares the combustion air, combining what would traditionally be separate processes into one unified operation that reduces overall system complexity.
3Loss of substance
If process air is partially ejected to atmosphere, then evaporated water is removed, but heat loss increases
Solution Approach 1:
The system discards only the necessary minimum amount of process air to atmosphere for water vapor removal, while recovering and recycling the majority of the process air back into the combustion system. This selective discarding and recovering approach minimizes heat loss while still achieving effective water removal from the paper.
4Temperature
If stoichiometric ratio is increased to 1.5-1.6 to control flame temperature, then nitrogen oxide emissions exceed limits, but flame temperature control improves
Solution Approach 1:
The patent changes the oxygen source parameter from atmospheric air to recycled process air enriched through steam cylinder contact. This parameter change enables maintaining the required flame temperature while operating at or near stoichiometric ratio, thereby eliminating excessive nitrogen oxide emissions that occur with higher air ratios.
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 significantly reduces heat losses, decreases pollutant emissions (CO and NOx), and achieves energy savings by optimizing combustion efficiency and air usage, resulting in a more effective and environmentally friendly drying process.
Implementation Method 1
a combustion chamber (38) provided with a burner (32) and configured to contain a flame produced by the burner (32) and developing in a mixture of process air and atmospheric air
Implementation Method 2
a cooling channel (34) provided at the rear terminal end of the combustion chamber (38) and configured to cool the combustion chamber (38)
Implementation Method 3
condensing, in the cooling channel (34), water vapor present in the process air
Implementation Method 4
a recirculation conduit (26) configured to convey a part of the process air extracted from the hood (12) back to the hot gas generator (14)
Data Source
Figure 1
Figure 2
AI summary
The present invention describes a system for drying a web-like paper sheet. The system comprises at least one drying device (12) capable of blowing high temperature dry air, supplied under pressure through one or more inlet conduits (20) on the web-like paper sheet, and of sucking from such a web-like paper sheet the moist air, ejected through one or more outlet conduits (22) connected to a recirculation conduit (26), and a combustion system (20) which comprises at least one hot gas generator (14) of the so-called direct type, provided with a system (16) for supplying fuel and a system (18) for supplying combustion air. The hot gas generator (14) consists of a burner (32), operatively connected to the system (16) for supplying fuel and to the system (18) for supplying combustion air, and of a combustion chamber (38) which is placed in direct fluid communication with the burner ( 32) by interposing a connection conduit (40). Outside the combustion chamber (38) at least one cooling channel (34) is provided, which encloses such a combustion chamber (38). The cooling channel (34) is placed downstream of the burner (32) and is operatively connected to the recirculation conduit (26), so that the hot gas generator (14) is capable of generating an air and burnt gases mixture which forms the dry air, as well as receiving, through such a recirculation conduit (26), at least part of the moist air so that it can be heated and reutilised by the drying device (12).