FABRIC
FILTER NEWSLETTER
May 1999
No. 283
Coal
Technology for the Next Century
Recently,
the U.S. Dept. of Energy unveiled a new concept, "Vision 21" — a
futuristic way of combining high-efficiency power technologies with advanced
coal processing technologies and environmental controls to create a near-zero
discharge, multi-product energy complex. A presentation at the 24th
International Technical Conference on Coal Utilization & Fuel Systems
outlined one conceptualization of a Vision 21 Plant that focuses on production
of hydrogen from coal. The information was provided by Joseph Badin of
Energetics, Incorporated, Michael DeLallo and Michael Rutkowski of Parsons
Corp., and Jerome Temchin of the U.S. Dept. of Energy. The concept can help
assure that coal can remain competitive with natural gas as a fuel for
baseload electricity generation for existing and new power plants. It can also
provide a feedstock for chemical and liquid fuels production, even if
emissions of carbon dioxide must be controlled.
Vision
21 is intended to develop the enabling technologies to allow the private
sector to combine high-efficiency power technologies with advanced coal
processing technologies and environmental control systems. Research on the
Vision 21 enabling technologies is expected to result in technology options
that could be introduced to the marketplace by 2020.
For
the longer term, new technologies are being developed to separate hydrogen
from syngas, resulting in the potential for hydrogen production at costs
competitive with natural gas. These technologies include inorganic membranes
to separate hydrogen from CO2,
high-temperature particulate filters, advanced turbine systems (ATS) and lower
cost air separation technologies such as ion transfer membranes. A conceptual
plant design was prepared, which utilizes some of the new technology to
provide a basis for producing lower cost hydrogen from coal.
The
system utilizes a high-temperature, high-pressure gasifier, a high-temperature
particulate filter and an advanced turbine system expander for power
generation. The key process is the hydrogen separation device, based on an
inorganic membrane under development by Oak Ridge National Laboratory.
The
high-pressure syngas produced in the gasifier is quenched to 1905°F as a
result of adjustments in the second stage of the gasifier, thereby eliminating
the requirement for a fire tube heat exchanger. The hot raw gas is cleaned of
larger particulates in a cyclone and has a considerable amount of steam added,
ensuring adequate water content for the high-temperature shift reaction to
occur, while reducing temperature to 1456°F. Following the cyclone, the gas
is cleaned of remaining particles with a ceramic candle filter. The gas enters
the hydrogen separation device (HSD) at 1456°F and leaves the HSD at 1823°F
as a result of the exothermic shift reaction. The hydrogen produced from the
HSD is 99.5 percent pure, and goes through a heat recovery steam generator (HRSG)
and cooler, resulting in hydrogen at 100°F and 15 psia. Product hydrogen is
compressed to 346 psia.
After
establishing a baseline design for production of hydrogen utilizing membrane
technology, additional conceptual plant designs utilizing variations in the
technology can be prepared. Included in the design variations being pursued
are:
Hydrogen
production utilizing a lower temperature gas and ceramic filter (about 1000°F)
ahead of the HSD. This approach places less stress on the ceramic filter and
ensures precipitation of alkali metal compounds prior to contact in the ATS
turbine expander.
Hydrogen
production utilizing hot gas desulfurization and a ceramic filter ahead of the
HSD. This concept protects the HSD and the turbine from alkali and sulfur
compounds and produces a marketable sulfur by-product.
Although
ceramic candle filters remain the most promising candidates for hot gas
particulate removal, both durability and long-term stability must be proven.
Long-term
durability at 1000° F has not been fully demonstrated, but the Piñon Pine
IGCC demonstration plant should provide these data. As operating data become
available, the upper limit of ceramic filters in reducing conditions should
increase. Filters can already be recommended for use at 1200°F in reducing
atmospheres. The filter for this application was assumed to operate at 1455°F
in a reducing atmosphere.