Gasification in Detail - Types of Gasifiers - Gasifiers for Special Applications
The Rocketdyne gasification technology program has an objective of applying technology developed and experience gained from rocket propulsion engines to coal gasification. Key technology components include: a rapid-mix feed injection system to facilitate rapid burning; an advanced reactor cooling system to mitigate the need of refractory lining; and a rapid spray quench system for raw syngas cooling. These attributes offer the potential of developing a very compact and low-cost gasifier, with high carbon conversion and increased thermal efficiency. Development of an advanced high-pressure, dry coal feed solids pump is also part of the Advanced Gasification System Development (AGSD) program activities. Figure 1 shows a simplified drawing of a Rocketdyne gasification system.
Figure 1: Conceptual Drawing of a Rocketdyne Gasification System
Pratt & Whitney Rocketdyne)
The Rocketdyne gasifier is a single-stage, pressurized, oxygen-blown, plug-flow entrained reactor capable of achieving carbon conversions approaching 100%. The gasifier uses Rocketdyne rocket technology to enable a compact, low-cost, long-life and highly efficient gasifier design.
The gasifier includes several design features borrowed from rocket fuel engine technology. Figure 2 shows the various components of a Rocketdyne gasifier that can be developed by patterning after similar, but well proven, features within a rocket engine. These include a rapid mix injector design that can use multi-element injection to rapidly mix the coal feed with steam and oxygen, and disperse them across the reactor cross section. By doing so, it enables the injected coal particles to be heated rapidly to high temperature, and allows the gasification reactions to take place in a very short residence time. This rapid mixing is said to greatly minimize the mass transfer and kinetic limitations to gasification reactions. The result is a gasification system that can achieve rapid and complete carbon conversion with less oxygen required. This feed injection system is being developed in conjunction with the development of a high-pressure solids pump and a dense phase flow splitter capable of bulk feeding and distributing the pulverized coal fines to the gasifier at high pressure.
Another engineering feature borrowed from the rocket engine experience is the gasifier cooling liner design, which allows the internal reactor wall to be cooled and protected by forming a layer of solidified slag on its inside surface. This type of ceramic matrix composite (CMC) liner helps to protect the refractory underneath, enabling an operational life much longer than the six- to 18-month life typically experienced for non-cooled refractory brick in existing gasifiers.
The high temperature raw syngas would need to be cooled to about 700 °F before entering a commercially available cyclone and candle-type filter for fly ash removal. This is accomplished by rapid spray quenching the produced raw syngas with water.
The Rocketdyne gasifier is expected to be able to process all different ranks of coal.
Figure 2: Attributes of a Rocketdyne Gasifier
(source: Pratt & Whitney Rocketdyne)
Current Developmental Demonstration Plan/Status
The AGSD Program has the following objectives:
- Demonstrate the feasibility of the rapid-mix injection system (both the injector and the dense phase flow splitter) at a commercial scale.
- Test and evaluate the performance of multiple CMC cooled refractory liner. This work is being done at CANMET Energy Technology Centre in Ottawa, Canada.
- Complete developmental work of a practical high-pressure, solids pump (Stamet technology) capable of delivering a dense-phase pulverized coal feed to a gasifier at 1,000 psia. Some of this effort is being carried out at the University of North Dakota’s Energy & Environmental Research Center in Grand Forks
- Complete preliminary integrated gasification combined cycle (IGCC) plant studies to identify a preferred gasifier configuration to use as the basis for a pilot plant design. GTI’s Flex-fuel Test Facility has been identified as the pilot plant site to demonstrate the integrated operation of this dry feed Rocketdyne gasification system with all its hardware.
Figure 3: AGSD Developmental Plan
(source: Pratt & Whitney Rocketdyne)