A downflow coal gasifier, supplied lime/limestone with the coal, removes sulfur and obviates the production of particulate matter in generating a clean, low BTU gas for the combustor of an MHD channel. Air for both the combustor of the MHD channel and the gasifier is heated by the discharged fluids from the channel.

TECHNICAL FIELD 
The present invention relates to the supply of gasified coal to a 
magnetohydrodynamic (MHD) generator of electric power. More particularly, 
the invention relates to gasifying coal while reducing the particulate and 
sulfur content of the low BTU gas and using the heat of the fluid output 
of an MHD channel, supplied by combusting the low BTU gas, to elevate the 
temperature of the air for both the channel combustor and the gasifier. 
BACKGROUND ART 
The MHD generator is well established in theory and practice as utilizing 
high temperature, high velocity, ionized fluid to generate electric power 
as the fluid is directed through a static magnetic field. Practicality 
dictates a temperature range for the gases of at least 4000 F. Potassium 
compounds, referred to as "seed," are injected into the combustion chamber 
for enhancing the ionization of the fluid flowing through the MHD channel. 
If an ample supply of clean fuel, such as gas and oil, is available and the 
combustion air can be brought up to a temperature of at least 2500 F., the 
resulting gaseous products of combustion after traversing the channel are 
ejected from the MHD channel and subsequently utilized to convert water to 
steam. The steam can then be used to power a turbine which is coupled to 
an electric generator. The total electric power generated by the MHD 
channel and steam cycle can then be compared to the energy input to the 
system to obtain an efficiency of approximately 50%. 
Coals is in abundant supply and it is, therefore, desirable that its energy 
be made available to the MHD generator. There are various systems for 
converting solid coal into relatively low BTU content gas for the MHD 
generator combustor. Unfortunately, coal-to-gas conversion runs into the 
vicious problem of compensating for the high ash and sulfur content of 
this form of fossil fuel. The ash is a polluting solid particulate in the 
final discharge to the atmosphere. Sulfur compounds may also be discharged 
to the atmosphere, as at least noxious pollutants, if not corrosive and 
poisonous threats to the environment. 
The present problem must be solved with a system which provides 
gasification of coal while reducing the particulate material and sulfur 
content of the gas to an acceptable level. Further, the combustion air 
required for the burning of the coal gas and its gasification must be 
heated by the discharge of the products of combustion from the MHD 
channel. Briefly, pollution to the environment is controlled and heat 
energy is conserved. 
DISCLOSURE OF THE INVENTION 
The present invention contemplates supplying fuel gas to an MHD channel 
from a downflow coal gasifier, fed a combination of coal and 
lime/limestone, burned sub-stoichiometrically, to produce a slag 
containing the sulfur of the coal and solid particulate while combustion 
air for the MHD combustor is heated in an exchanger in the vapor output of 
the MHD diffuser. Further, the invention contemplates the air for 
producing the coal gas has its temperature, also, elevated by exchange 
with the fluid products of combustion from the MHD channel, itself. 
Other objects, advantages, and features of the invention will become 
apparent to one skilled in the art upon consideration of the written 
specification, appended claims and accompanying drawing.

BEST MODE FOR CARRYING OUT THE INVENTION 
Broadly Speaking 
The end function of the system depicted in the drawing is to gasify coal in 
tower 10 and supply this fuel as a clean, low BTU gas to combustor 11 of 
MHD channel 12. Electrical energy will be generated by the channel 12 and 
the gaseous products of combustion from the combustor 11 will be 
discharged to a steam generator 13. The steam generated at 13 will be 
discharged at 14 and be utilized in a turbine-electric generator connected 
to conduit 14 to produce additional electrical energy. Therefore, the end 
result of the system is to convert the energy in coal to electrical energy 
with an efficiency of approximately 50%. 
The Sulfur Problem and Solution 
One of the problems faced by the present invention is to control the amount 
of sulfur compounds ultimately discharged to the atmosphere. Conduit 20 
represents the means for withdrawing the exhaust gases from generator 13 
by fan 21 and delivering them to a stack by way of conduit 22. Sulfur 
compounds, which have their origin in the coal, are removed from the 
process by their discharge through conduit 25 which forms an exit from the 
lower portion of gasifier tower 10. Coal is supplied to the gasifier from 
a storage 26. The coal is mixed with lime/limestone and this mixture 
supplied through conduit 27 connected between the storage and upper 
portion of the tower 10. The coal is burned with heated air under 
sub-stoichiometric conditions in the upper portion of tower 10, the 
lime/limestone combining with the sulfur compounds of the coal and forming 
part of the slag removed through conduit 25. 
The low BTU gaseous product of the coal is flowed from the lower portion of 
tower 10 through conduit 30. This low BTU (circa 150 BTU/cu. ft.) gas is 
supplied combustor 11. Thus, the sulfur contaminant and particulate matter 
is reduced at this early stage within the system disclosed, and the final 
discharge to the stack through conduit 22 will meet present environmental 
standards. 
The Coal Gasifier 
The structure depicted as within tower 10 is a vital element of the 
embodiment of the present invention, if not its raison d'etre. This unique 
structure provides its clean fuel gas product by downflowing the coal and 
lime/limestone and combustion air supplied the upper portion of tower 10. 
The details of the structure needed to carry out the sub-stoichiometric 
combustion and formation of sulfur and particulate absorption slag is 
disclosed in U.S. Fernandes' U.S. Pat. No. 3,920,417 issued Nov. 18, 1975. 
The disclosure of this patent is incorporated and made a part of this 
present disclosure by reference. The operation and structural arrangement 
of this unit within tower 10 is to be in accordance with the teachings of 
this patent disclosure. To incorporate this disclosure, the present 
invention concerns itself only with the facts that the lime/limestone and 
coal of source 26 and heated combustion air are supplied the upper portion 
of tower 10 while slag and clean coal gas are removed from the lower 
portion of tower 10. 
Heating Combustion Air 
The generation of gaseous fluid as a product of combustion within 11 is 
well developed in the art. The combustion is controlled to produce a 
gaseous fluid with a temperature of at least 4000 F. for high velocity 
flow through channel 12. To reach this temperature, it is necessary that 
the combustion air supplied combustor 11 be preheated to a temperature 
which will insure the ionization of the fluid discharged through channel 
12. Of course, the flame temperature within the combustor 11 may be 
elevated by supplementing the heat to its combustion air with oxygen 
enrichment. The combination of heat and oxygen to the combustion air is 
grist for the economic mill with which the complete system is engineered. 
Further, seed, in the form of potassium sulfide or potassium carbonate, is 
introduced from a supply through conduit 32 connected to the combustor. 
For economic reasons, this expensive material is recovered downstream of 
the channel and recycled. The seed is vaporized to pass through channel 12 
and subsequently condensed at the lower downstream temperatures. The 
present invention is not directly concerned with the mechanics of cooling 
the condensed seed and recycling it to the combustor. However, it is 
recognized that a cyclone operating at temperatures as high as 2000 F., or 
granular filters, may be employed in the recovery cycle. 
The high temperature, ionized, gaseous fluid discharged from channel 12 
flows through diffuser 35. A conduit 36 represents the path for this fluid 
into vapor generator 13. The complication of heat exchange surfaces 
between this gaseous fluid and water to generate steam need not be shown. 
It is sufficient to indicate that feed water flows into this generator 13 
from a source through conduit 37 and emerges as steam through conduit 14. 
Additionally, the seed introduced through conduit 32 is condensed and 
collected within generator 13 and extracted through conduit 38. 
The gaseous fluid from the MHD generator flowing into steam generator 13 
through conduit 36 may have its heat supplemented by burners within the 
generator 13. The provision for supplemental burners is additionally 
indicated by conduit 41 supplying secondary air for the burner operation 
with fan 42. Whatever the specific arrangement for extracting heat from 
the fluid output of the MHD channel and burners, there is included, heat 
exchange surfaces for transfer of a part of this heat to air conducted 
through conduit 39 by compressor 40. The heating of this air within 
generator 13 is continued by conducting it through conduit 50 and passing 
it through exchanger 51. 
There is invention in the system for supplying the combustion air for 
combustor 11 and the sub-stoichiometric combustion in tower 10. The air in 
conduit 52 is supplied for both uses. It has been conventional to heat the 
air for these services by an independently-fired preheater. However, in 
the present invention, sufficient heat is supplied to the air in conduit 
50 by heat exchanger 51. Heat exchanger 51 is placed at the output of 
diffuser 35. The technology of heat exchangers has evolved until the heat 
exchanger 51 has a practical form for exposure to the high temperature 
gaseous output of channel 12. It is now practical for the air passed 
through conduit 50 to be flowed through exchanger 51 and have its 
temperature elevated to at least 2000 F. Output conduit 52 of exchanger 51 
is then connected to first branch 53, conduit 53 conducting the portion of 
the air needed for the sub-stoichiometric combustion in tower 10. Branch 
conduit 54 concomitantly conducts its portion of the air from conduit 52 
to combustor 11. As indicated previously, the combustion air in conduit 54 
may have its oxygen content elevated as a supplement to its heating by 
exhanger 51. This provision is not shown, but is a well-known arrangement 
for control of the flame temperature within combustor 11. 
Conclusion 
The present embodiment extracts the energy of coal and converts it to 
electrical energy. In carrying out this conversion, sulfur, which is found 
in most coal supplies, is quickly removed in a gasifier 10 as a component 
of the slag removed through conduit 25. This early removal of the sulfur 
solves problems downstream. The combination of the sulfur with the 
potassium seed material is obviated and its subsequent removal from the 
discharge gases of the stack through conduit 22 is avoided. 
The present system eliminates the need for an independently-fired preheater 
of the combustion air to combustor 11 and tower 10. The necessary heat is 
extracted from the working fluid discharged from channel 12. Heat 
exchanger 51 can be given the practical form for this heat transfer and 
thereby eliminate the complication of a separately-fired preheater. 
From the foregoing, it will be seen that this invention is one well adapted 
to attain all of the ends and objects hereinabove set forth, together with 
other advantages which are obvious and inherent to the apparatus. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
invention. 
As many possible embodiments may be made of the invention without departing 
from the scope thereof, it is to be understood that all matter herein set 
forth, or shown in the accompanying drawing, is to be interpreted in an 
illustrative and not in a limiting sense.