Rotary Grate with Conical Slots for Gasifier Ash Clogging
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Solution Overview
Problem
Fixed-bed gasifiers face clogging issues due to biomass particles and ash falling through or getting stuck in the grate openings, especially when product gas flows from top to bottom, leading to reduced efficiency and operational challenges.
Innovation Solution
A rotatable grate with slot-shaped openings that vary in size and are designed conically, allowing ash and slag to be crushed and pushed through, while the dome-shaped cover prevents accumulation, and the grate's rotation shears off ash laterally, reducing clogging risks. The rotational speed and time intervals of the grate further mitigate clogging, ensuring even air distribution and flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the grate openings are made small to support biomass particles, then particle support is improved, but the risk of clogging by ash and tar increases
Solution Approach 1:
The grate is designed to rotate about a vertical axis, transforming from a static structure to a dynamic one. This rotation creates variable relative motion between the grate surface and the biomass/ash particles, preventing accumulation and clogging while maintaining adequate support functionality.
Solution Approach 2:
The grate undergoes periodic rotation cycles, creating alternating periods of particle support and ash removal. During rotation, ash particles are periodically discharged from the grate surface, preventing continuous clogging while maintaining particle support during the support phase.
2Productivity
If the grate openings are made large to allow ash and gas flow, then flow efficiency is improved, but biomass particles may fall through or become trapped
Solution Approach 1:
The rotating grate creates dynamic conditions where the effective opening size varies with rotation position. At certain rotation angles, larger openings facilitate ash and gas flow, while at other angles, the grate geometry provides particle retention, balancing both requirements.
Solution Approach 2:
The grate structure employs different opening characteristics in different regions. The slot-shaped openings have specific dimensional properties that allow differentiation between regions needed for particle support versus regions optimized for ash and gas flow during rotation.
3Device complexity
If the grate is stationary to simplify design, then structural simplicity is improved, but clogging risk increases under unfavorable operating conditions
Solution Approach 1:
The grate transitions from a stationary to a rotating structure, adding motion capability to prevent clogging. The rotation mechanism, driven by a motor, creates variable flow conditions that actively prevent ash and tar accumulation without requiring complex additional components.
Solution Approach 2:
The rotating grate performs dual functions: supporting biomass particles during gasification and automatically removing ash through rotation-driven discharge. This self-service capability eliminates the need for separate ash removal mechanisms, maintaining relative structural simplicity while preventing clogging.
4Productivity
If product gas flows from top to bottom through the grate, then gasification efficiency is improved, but clogging of grate openings is exacerbated
Solution Approach 1:
The rotating grate creates dynamic flow patterns that alternate between top-to-bottom gas flow (for efficient gasification) and conditions that promote ash discharge. The rotation prevents continuous clogging by periodically clearing the grate surface while maintaining the necessary gas flow path for gasification efficiency.
Solution Approach 2:
The system operates in periodic cycles where gas flows through the grate for gasification, followed by rotation-driven ash removal phases. This periodic alternation maintains gasification efficiency while preventing cumulative clogging that would occur with continuous top-to-bottom flow through a stationary grate.
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 design significantly reduces clogging, maintains efficient ash and product gas flow, and produces a product gas with low tar content by ensuring uniform gas and air distribution across the oxidation zone, enhancing the overall operation of the gasifier.
Implementation Method 1
The rotating grate acts as a planer, breaking up lumps of ash and slag, which are then forced through the slotted openings by the rotational movement
Implementation Method 2
The conical design of the openings in the rotating grate significantly reduces the risk of clogging by ash and product gas
Implementation Method 3
The central dome-shaped cover prevents ash or slag from accumulating in the center of the main section due to the limited or non-existent movement of the grate relative to the biomass
Implementation Method 4
Fixed-bed gasifiers are divided into different reaction zones, namely drying, pyrolysis, oxidation, and reduction zones, in which various thermochemical reactions take place
Implementation Method 5
Fixed-bed gasifiers are divided into different reaction zones, namely drying, pyrolysis, oxidation, and reduction zones, in which various thermochemical reactions take place
Data Source
Figure 1
Figure 2~3
AI summary
The invention provides a grate that can be flowed through from above and is intended for supporting the biomass particles and for drawing off ash and product gas, with a reduced tendency for the openings in the grate to become clogged. The invention also provides a fixed-bed gasifier with such a grate. The rotation of the grate has the effect that it acts as a plane and that lumps of ash and slag are broken up and forced through the slit-shaped openings by the rotational movement. The slit shape of the openings means that, in spite of a large passing-through area, even small biomass particles can be supported. The conical shaping of the openings in the rotary grate means that the risk of the slit-shaped openings for ash and product gas becoming clogged is reduced considerably and the slit-shaped openings act like a plane. The central dome-shaped covering prevents any accumulation of ash or slag in the middle of the main part being caused by the grate moving little or not at all with respect to the biomass. It should also be considered in this respect that there may be no openings in the middle, since the drive shaft is attached or mounted in the middle of the main part. The dome-shaped configuration of the covering means that the rotation of the grate causes ash and slag to be sheared off laterally, so that they are transported into the region with the slit-shaped openings.