Method and System for Controlled Gasification

Inactive Publication Date: 2012-02-02
AIR PROD & CHEM INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0009]One aspect of the present disclosure includes a method of controlled gasification. The method includes introducing a first fuel to a gasifier in a system, introducing a first fuel to a gasifier in a system, generating a product gas by partially oxidizing the first fuel with an oxidizer including oxygen, directing a first portion of the product gas to a

Problems solved by technology

Further, gasification of the solid fuel is preceded by heating of the fuel, and this heating requires a significant amount of time, the exact amount depending upon the fuel feed size, porosity, and density, as well as the gasification system design and operating conditions.
Moreover, many solid fuel gasification systems, such as fluidized or non-fluidized bed designs, contain large amounts of stored mass (for example, from fuel and ballast material such as sand).
The response of solid fuel gasification systems is often sluggish or slow, particularly when a low energy density feedstock with relatively large particle feedstock is employed.
This sluggishness hampers the ability of solid fuel gasification systems to adequately satisfy the time-varying demand needs of many industrial processes.
Moreover, the mass transport and mixing processes in solid fuel gasification systems are relatively slow and generally more sensitive to changes in flow rate (occurring with changes in operating conditions) than in gaseous-based gasifiers (partial oxidizers) and liquid-based gasifiers.
Further, due to the large inertia of solid fuel gasification systems, the true effect of attempting turndown in such systems is typically delayed, sometimes by several minutes or more.
This can create a false sense of safety and stability in the mind of system operators, which can ultimately lead to more catastrophic effects.
In slagging gasifiers, for example, time-delayed slag solidification can occur on turndown, creating a bottleneck in reactor flows that often results in a complete system shutdown.
The aforementioned limitations on transient response and turndown of solid fuel systems represent technical hurdles in the application of solid fuel gasification systems to dedicated processes, such as boilers and furnaces that must frequently respond to time-varying energy or production demands.
Shortcomings in these approaches include lower efficiency associated with flaring unused syngas, additional cost and complexity associated with multiple reactors, and relatively high operating cost and / or lack of availability of back-up fuels.
The method and apparatus fail to address the above-described drawbacks.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

Low Syngas Heating Value

[0065]In a first Example, measurement of the syngas composition reveals that the CO concentration decreases by 5 mol % while the CO2 concentration increases by the same percentage as a result of the first adjustment step 730, lowering the syngas HHV to 294.5 Btu / scf (see Table 7 for a breakdown of the system 100 parameters, including syngas properties, energy and mass flows before and after the gasifier control step 720 actions).

TABLE 7Key System Parameters for Example 1: Low Syngas HHVState 1a: Following FirstAdjustment Step 730but Prior to GasifierState 1b: FollowingSyngas ComponentControl Step 720Gasifier Control Step 720CO50mol %55mol %H225mol %20mol %CH45mol %10mol %CO210mol %5mol %N25mol %5mol %H2O5mol %5mol %Syngas HHV294.5Btu / scf344.8Btu / scfGasifier2080°F.2050°F.TemperatureEnergy to Boiler190MMBtu / hr190MMBtu / hrEnergy out of222.2MMBtu / hr222.2MMBtu / hrGasifierSyngas Recycle32.2MMBtu / hr32.2MMBtu / hrEnergySolid Fuel Energy229.2MMBtu / hr229.2MMBtu / hrGasifier ...

example 2

Low Gasifier Temperature

[0067]In a second Example, the syngas heating value remains within the predetermined range, but the gasifier temperature is lowered to 1980° F., which is lower than a desired range based on slagging considerations. This can happen for several reasons, such as lower feedstock quality or higher gasifier dilution resulting from the higher ratio of syngas to solid feedstock energy input relative to baseline conditions. The oxygen flow rate is adjusted (box 716) to increase the gasifier oxygen flow rate, thereby oxidizing more of the fuel inside the gasifier and releasing more thermal energy. The stoichiometric ratio φ thus incrementally increases until the gasifier temperature rises back above 2000° F. A value of φ equal to 0.27 results in a gasifier temperature of 2020° F. while maintaining the syngas HHV above 300 Btu / scf. System 100 parameters of the gasifier 300 for the second Example are provided in Table 8.

TABLE 8Key System Parameters for Example 2: Low Gas...

example 3

High Gasifier Temperature

[0068]In a third Example, high gasifier temperature results from first adjustment step 730 actions. Measurement of the gasifier temperature (box 710) detects the high temperature condition. The control system 305 responds by reducing the syngas recycle flow rate (box 714), since this lowers the total energy input to the gasifier 300 without affecting the energy delivered to the boiler. System 100 parameters corresponding to the initial and final condition for this case are summarized in Table 9.

TABLE 9Key System Parameters for Example 3: High Gasifier TemperatureState 3a: Following FirstAdjustment Step 730Syngasbut Prior to GasifierState 3b: FollowingComponentControl Step 720Gasifier Control Step 720CO55mol %55mol %H225mol %25mol %CH45mol %5mol %CO25mol %5mol %N25mol %5mol %H2O5mol %5mol %Syngas HHV310.5Btu / scf310.5Btu / scfGasifier2230°F.2180°F.TemperatureEnergy to Boiler190MMBtu / hr190MMBtu / hrEnergy out of222.2MMBtu / hr215.9MMBtu / hrGasifierSyngas Recycle32.2MM...

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Abstract

Disclosed is a system and a method of controlled gasification. The method includes introducing a first fuel to a gasifier in a system, introducing a first fuel to a gasifier in a system, generating a product gas by partially oxidizing the first fuel with an oxidizer including oxygen, directing a first portion of the product gas to a process chamber, and selectively introducing a recycled portion of the product gas to the gasifier.

Description

BACKGROUND OF THE INVENTION[0001]The present invention is directed to gasification. More specifically, the present invention relates to a method and system for controlled gasification in a system having product gas recycle.[0002]Most solid fuel gasification systems contain substantial thermal inertia relative to comparable liquid and gaseous fuel systems. Further, gasification of the solid fuel is preceded by heating of the fuel, and this heating requires a significant amount of time, the exact amount depending upon the fuel feed size, porosity, and density, as well as the gasification system design and operating conditions. Moreover, many solid fuel gasification systems, such as fluidized or non-fluidized bed designs, contain large amounts of stored mass (for example, from fuel and ballast material such as sand). The response of solid fuel gasification systems is often sluggish or slow, particularly when a low energy density feedstock with relatively large particle feedstock is emp...

Claims

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Application Information

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IPC IPC(8): C10J3/48C10J3/46
CPCC10J2300/1823C10J3/723
InventorD'AGOSTINI, MARK DANIELO'NEILL, CHRISTOPHER
OwnerAIR PROD & CHEM INC