Steam power plant

A steam power plant for producing energy from tarry residual oils from a refinery includes a steam generator as well as a combustion system heating the steam generator and having a fuel side. A fired tubular furnace for heating high-viscosity refinery residues to 400.degree. to 600.degree. C., for instance, produces gaseous and vaporous products and other components of the residue. A separating column connected downstream of the fired tubular furnace separates the gaseous and vaporous products from the other components of the residue. The separating column has a lower end and an outlet line at the lower end connected upstream of the fuel side of the combustion system for the other components of the residue.

The invention relates to a steam power plant having a steam generator 
heated by a combustion system. 
The steam generators of such steam power plants can often be heated with 
heavy oil. Although this kind of heating requires less capital investment 
than heating with pulverized coal, for instance, it entails relatively 
high fuel costs. 
In petroleum refineries, the crude oil is split in separating columns 
connected in series with one another into various fractions which differ 
according to their boiling points. What is left at the end is a residue of 
highly viscous to tarry consistency, which is difficult to sell. Usually, 
it is used in the asphalt industry. Attempts to burn this more-expensive, 
high-viscosity refinery residue in power plants have thus far been aimed 
in two different directions: 
First, mixing these high-viscosity refinery residues with more valuable, 
less-viscous fractions was attempted, in order to reduce their viscosity 
enough that they could again be pumped at temperatures that were 
not-excessively high and atomized in burners. However, the trade-off was 
that some of the cost advantage of these highly-viscous refinery residues 
was lost. 
Pumping these high-viscosity refinery residues at correspondingly high 
temperatures, at which they are still fluid, and then burning them after 
heating them further, was also tried. However, since proper combustion is 
possible only after such hydrocarbons are atomized, but atomization 
requires an even lower viscosity (approximately 25 cSt) than that which is 
sufficient for pumping, further heating prior to combustion is necessary. 
However, at the high temperature required for this, the danger of 
uncontrolled ignition is increased. Furthermore, because of the high 
temperature level required, such heating necessitates tapping into the 
high-pressure portion of the steam turbine, or using fresh steam. A 
further factor making the entire procedure more difficult is that sulfur 
and components that cause corrosion are present in concentration in these 
high-viscosity residues. The flue gas produced after combustion can cause 
both high-temperature and low-temperature corrosion. 
It is accordingly an object of the invention to provide a steam power 
plant, which overcomes the hereinafore-mentioned disadvantages of the 
heretofore-known devices of this general type and which permits the 
highly-viscous refinery residues to be reasonably combusted completely in 
the power plant. Moreover, the cost advantage of these refinery residues 
should not be wasted by excessively high expenses in the power plant nor 
by the additional purchase of more-expensive fuels. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, a steam power plant, comprising a steam 
generator, a combustion system heating the steam generator and having a 
fuel side, a pipe furnace for heating high-viscosity refinery residues to 
400.degree. to 600.degree. C., for instance, and producing gaseous and 
vaporous products and other components of the residue, and a separating 
column connected downstream of the pipe furnace for separating the gaseous 
and vaporous products from the other components of the residue, the 
separating column having a lower end and an outlet line at the lower end 
connected upstream of the fuel side of the combustion system for the other 
components of the residue. 
Since the fuel side of the combustion system of the steam generator is 
preceded by a pipe furnace for heating high-viscosity refinery residues to 
400.degree. to 600.degree. C., which is followed by a separating column 
for separating the gaseous and vaporous products of the other residue 
components, with the outlet line for the other residue components 
connected from the lower end of the separating column to the combustion 
system of the steam generator, these high-viscosity refinery residues can 
be utilized for steam generation without being mixed with more-expensive, 
lighter-weight refinery products. Thermal cracking takes place in the pipe 
furnace, which breaks apart the long hydrocarbon chains that are 
responsible for the high viscosity. The result is a mixture of 
hydrocarbons of overall reduced viscosity. This viscosity is reduced to 
such an extent that even the fraction that can be drawn off from the lower 
end of the separating column can be pumped and stored at a substantially 
lower temperature and no longer needs to be heated as much for combustion 
in heavy-oil burners. 
Although it is known in the petrochemical industry to crack the 
distillation products of higher viscosity at increased temperatures in 
order to increase the yield of light weight fractions, nevertheless a 
high-viscosity residue is always left, which previously could only be sold 
essentially to the asphalt industry. However, by using the technology for 
heavy oil combustion, the invention of the instant application makes it 
possible to utilize this portion completely for energy production as well. 
In accordance with another feature of the invention, the separating column 
has an upper end and another outlet line at the upper end, and there is 
provided a condensation apparatus into which the other outlet line 
discharges, the condensation apparatus having a top product serving as 
heating medium for the pipe furnace. This provision makes it unnecessary 
to purchase a special heating medium for operating the pipe furnace. 
In accordance with a further feature of the invention, the condensation 
apparatus has a lower end from which a product is drawn off and supplied 
to the combustion system. By mixing the less-viscous fraction obtained in 
the cracking process, a further reduction in the viscosity of the fraction 
drawn off at the lower end of the separating column and fed into the 
combustion chamber of the steam generator is attained. 
In accordance with an added feature of the invention, there is provided a 
gas turbine power plant connected upstream of the steam generator for 
feeding exhaust gases as heat transfer and oxygen carrying media to the 
combustion system, the gas turbine power plant having a gas turbine and a 
combustion chamber connected to the gas turbine; and a condensation 
apparatus having a lower end from which a product is drawn off and 
supplied as fuel to the combustion chamber. 
This provides a particularly advantageous structure, which at the same time 
brings particularly high efficiency of the power plant. In this case, the 
already very high overall efficiency of a combined gas and steam turbine 
power plant is augmented by the advantage that the gas turbine can 
likewise be driven, although indirectly, by the high-viscosity refinery 
residues, since the corrosive components of the product used remain in the 
heavy residues that are drawn off at the lower end of the separating 
column and thus do not reach the particularly vulnerable gas turbine. 
In accordance with an additional feature of the invention, there is 
provided a reservoir, and another outlet line directly connected between 
the reservoir and the lower end of the condensation apparatus for the 
product drawn off at the lower end of the condensation apparatus, the 
other outlet line also being connected from the reservoir to the 
combustion system and the combustion chamber as well in the embodiment 
having a combustion chamber. 
In accordance with yet another feature of the invention, there is provided 
a reservoir directly connected between the outlet line and the combustion 
system for the other components of the residue from the lower end of the 
separating column. 
In accordance with yet a further feature of the invention, the pipe furnace 
heats the refinery residues to 450.degree. to 500.degree. C. 
In accordance with a concomitant feature of the invention, the separating 
column and the condensation apparatus are combined. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
steam power plant, it is nevertheless not intended to be limited to the 
details shown, since various modifications and structural changes may be 
made therein without departing from the spirit of the invention and within 
the scope and range of equivalents of the claims.

Referring now to the figures of the drawing in detail and first, 
particularly, to FIG. 1 thereof, there is seen a steam turbine power plant 
1, preceded by a system 2 for preparing high-viscosity refinery residues. 
As can be seen in the schematic drawing of the steam turbine power plant, 
a feedwater container 3 is connected in series with a feedwater pump 4, a 
feedwater preheater 5, a steam generator 6 and a superheater 7, and a 
high-pressure steam turbine 8 is connected to the superheater. A steam 
vent line 9 of the high-pressure steam turbine 8 is connected through an 
intermediate superheater 10 to a medium-pressure steam turbine 11 and a 
low-pressure steam turbine 12. A steam vent line 13 of the low-pressure 
steam turbine 12 is connected to a condensor 14, which communicates 
through a condensate pump 15 with the feedwater container 3. The steam 
vent line 9 of the high-pressure steam turbine 8 is also connected to the 
feedwater preheater 5 and the feedwater container 3. The high-pressure, 
medium-pressure and low-pressure steam turbines, along with a generator 16 
that is to be driven, are all mounted on a common shaft 17. 
The system 2 for preparing the high-viscosity refinery residues includes a 
pipe furnace 18, a separating column 19 connected thereto, a condensation 
apparatus 21 which is connected to an outlet line 20 on the top of the 
separating column 19 and may also be combined with the separating column, 
and a reservoir 22 for a liquid fraction drawn off at the lower end of the 
condensation apparatus 21 by means of a feed pump 23. An outlet line 24 on 
the top of the condensation apparatus 21 is connected to a fuel supply 
line 25 of the pipe furnace 18. An outlet line 26 at the lower end of the 
separating column 19 is provided with a feed pump 27 and is connected to a 
combustion system in the form of heavy oil burners 28 of the steam 
generator 6. Once again, a reservoir can be disposed between them. Also 
discharging into the burners is a fresh-air line 29, which is supplied by 
a motor-driven fresh-air blower 30. On the outlet side, the reservoir 22 
is also connected to the outlet or fuel line 26 leading to the heavy oil 
burners 28 of the steam generator. 
When the steam turbine power plant 1 is operating, preheated, 
high-viscosity refinery residues enter the pipe furnace 18 in a manner 
which is not shown in further detail herein, and are heated there to 
between 450.degree. and 500.degree. C. in the exemplary embodiment. The 
lengths of heating coils in the pipe furnace are selected as a function of 
the intended flow speed in such a way that the high-viscosity refinery 
residues are exposed for several minutes to a temperature above 
450.degree. C. At this temperature, the long molecular chains break, 
producing shorter and even quite short hydrocarbon chains. In the course 
of this process, the viscosity is greatly reduced. The mixture of 
hydrocarbons which is thus formed and which flows well at this temperature 
reaches the separating column 19. There, it is separated into a gaseous or 
vaporous fraction that can be drawn off at the top of the separating 
column, and a liquid fraction that collects at the lower end of the 
separating column 19. The gaseous and vaporous component that can be drawn 
off at the top of the separating column 19, at approximately 400.degree. 
to 450.degree. C. in the exemplary embodiment, is then cooled down in the 
condensation apparatus 21, which is constructed as a separating column, to 
approximately ambient temperature. A fraction which is liquid at this 
temperature collects at the lower end of the condensation apparatus 21. A 
gaseous fraction can also be drawn off at this temperature at the top of 
the condensation apparatus. This gaseous fraction is drawn off at the top 
of the condensation apparatus 21 through the outlet line 24 and supplied 
to the pipe furnace 18 as fuel. The fraction produced at the lower end of 
the separating column 19, which is liquid at the temperature of 
approximately 400.degree. C. prevailing there, is pumped through the 
further feed pump 27 into the heavy oil burners 28 of the steam generator 
6, where it is combusted together with the fresh air pumped by the 
fresh-air blower 30. It could also be temporarily stored in a heated 
reservoir 72 and drawn out as needed. The liquid fraction collecting at 
the lower end of the condensation apparatus 21 is pumped through the feed 
pump 23 into the reservoir 22. It can be drawn off from there as needed 
and mixed into the line 26 leading to the heavy oil burners 28. However, 
it can also be delivered for some other separate use instead. 
The steam produced in the steam generator 6 is dried and superheated in the 
superheater 7 and carried into the high-pressure steam turbine 8. The 
exhaust steam of the high-pressure steam turbine is reheated in the 
intermediate superheater 10 and is supplied as medium-pressure steam to 
the medium-pressure steam turbine 11 mounted on the common shaft 17 and to 
the low-pressure steam turbine 12 connected in series with the 
medium-pressure steam turbine 11. The exhaust steam of the low-pressure 
steam turbine 12 is condensed in the condensor 14, and the condensate 
produced is pumped through the condensate pump 15 into the feedwater 
container 3. The feedwater is pumped from the feedwater container through 
the feedwater pump 4 into the feedwater preheater 5 and from there back 
into the steam generator. The feedwater preheater 5 may be heated by a 
portion of the exhaust steam of the high-pressure steam turbine 8, which 
is diverted from the exhaust steam line 9. 
With this kind of construction of a steam turbine power plant 1, the power 
plant can be driven with the high-viscosity refinery residues that 
otherwise are difficult and therefore expensive to use (for instance in 
the asphalt industry). The additional expense required for this purpose, 
in the form of a system 2 for preparing high-viscosity refinery residues, 
is within limits and does not require additional fuels. 
The exemplary embodiment of FIG. 2 has a steam turbine power plant 31 
preceded by a gas turbine power plant 32 and a system 33 preceding both of 
them, for preparing high-viscosity refinery residues. The gas turbine 
power plant 32 includes a gas turbine 34 having an air compressor 36, a 
generator 37 mounted on the same common shaft 35, and a combustion chamber 
39 connected to a fresh-air line 38 of the air compressor. 
Similarly to the exemplary embodiment of FIG. 1, the steam turbine power 
plant 31 has high-pressure, medium-pressure and low-pressure steam 
turbines 41, 42 and 43, respectively, mounted on the same common shaft 40 
and driving a generator 44. Connected to an associated feedwater container 
45 of the steam turbine power plant 31 are a feedwater pump 46, a 
feedwater preheater 47 and a steam generator 48 having superheater heating 
surfaces 49. As in the exemplary embodiment of FIG. 1, the steam generator 
48 is heated by a combustion system in the form of heavy oil burners 50. 
The hot exhaust gases from the gas turbine 34 are supplied through an 
exhaust line 51 to the heavy oil burners and serve as oxygen carriers for 
the burners. The exhaust gases leave the steam generator 48 at relatively 
high temperature and are therefore subsequently utilized for feedwater 
preheating in a feedwater preheater 52. This flue-gas-heated feedwater 
preheater 52 is connected in parallel with the previously mentioned 
feedwater preheater 47, which is heated by a portion of the exhaust steam 
of the high-pressure steam turbine 41. An exhaust steam line 53 of the 
high-pressure steam turbine 41 is connected through an intermediate 
superheater heating surface 54 to the medium-pressure steam turbine 42. An 
exhaust steam line 55 of the low-pressure turbine 43 leads into a 
condensor 56. Connected to the condensor 56 is a condensate line 58 
leading to the feedwater container 45 and being equipped with a condensate 
pump 57. 
The system 33 for preparing high-viscosity refinery residues is identical 
to the equivalent system 2 of the exemplary embodiment of FIG. 1 and 
therefore includes a pipe furnace 60, a separating column 61 connected 
thereto, a condensation apparatus 63 connected to an outlet line 62 at the 
top of the separating column, and a reservoir 64 for the liquid fraction 
drawn off by a feed pump 65 at the lower end of the condensation apparatus 
63. The condensation apparatus 63 may also be combined with the separating 
column 61. Once again, the gaseous fraction drawn off at the top of the 
condensation apparatus through an outlet line 66 is supplied to the pipe 
furnace 60 as fuel, and an outlet line 68 for the liquid fraction drawn 
off at the lower end of the separating column is connected through a 
further feed pump 67 and optionally through a reservoir 74 to the steam 
generator 48 of the steam turbine power plant 31. However, contrary to the 
exemplary embodiment of FIG. 1, a fuel line 70 leading back to the 
reservoir 64, for the fraction which is liquid at ambient temperature in 
the exemplary embodiment, is additionally connected to the combustion 
chamber 39 of the gas turbine 34. 
In operation of the gas and steam turbine power plant of the exemplary 
embodiment of FIG. 2, the gas turbine 34 is driven with the fraction at 
the lower end of the condensation apparatus 63. The fraction is drawn from 
the reservoir 64 and is liquid at ambient temperature. This liquid 
fraction is combusted in the combustion chamber 39 with the fresh air from 
the air compressor 36 of the gas turbine power plant 32 and supplied to 
the gas turbine 34. The air compressor and the generator 37 mounted on the 
same shaft 35 are driven in this process. The exhaust gas from the gas 
turbine flows as a heat transfer medium and oxygen carrier into the heavy 
oil burners 50 of the steam generator 48 of the steam turbine power plant 
31 and then, as flue gas, through the feedwater preheater 52. The heavy 
fraction drawn off at the lower end of the separating column 61 is pumped 
through the feed pump 67 into the heavy oil burners 50 of the steam 
generator 48. 
As in the exemplary embodiment of FIG. 1, the steam generated in the steam 
generator 48 and dried and superheated in the superheater 49 is supplied 
to the high-pressure steam turbine 41 and is carried through the 
intermediate superheater 54 into the medium-pressure steam turbine and 
from there into the low-pressure steam turbine. These three steam turbines 
drive the generator 44 mounted on the same shaft 40. The exhaust steam of 
the low-pressure steam turbine 43 is condensed in the condensor 56. The 
condensate is pumped through the condensate pump 57 into the feedwater 
container 45, and the feedwater is pumped back through the feedwater pump 
46 into the feedwater preheaters 47, 52 and to the steam generator 48. In 
this process, shown in FIG. 2, a portion of the feedwater is preheated 
through the flue-gas-heated feedwater preheater 52. As a result, an 
additional quantity of steam is available to the medium-pressure steam 
turbine 42 and the low-pressure steam turbine 43, as compared with the 
exemplary embodiment of FIG. 1. 
In this gas and steam turbine power plant, the combustion chamber 39 of the 
steam turbine 34 is operated with the fraction at the lower end of the 
condensation apparatus 63, which is liquid at ambient temperature. 
Depending on the power required, a corresponding larger or smaller 
quantity of fuel can be drawn from the reservoir 64. There is also the 
option of mixing this fraction, which is liquid at ambient temperature, 
with the fraction in the outlet line 68, which is liquid at the elevated 
temperature of the separating apparatus 61, and thus to further reduce its 
viscosity. If there is a malfunction in the gas turbine system, the steam 
block can also be operated independently, with a fresh-air blower 69. 
The foregoing is a description corresponding in substance to German 
Application P 38 14 242.2, dated Apr. 27, 1988, the International priority 
of which is being claimed for the instant application, and which is hereby 
made part of this application. Any material discrepancies between the 
foregoing specification and the aforementioned corresponding German 
application are to be resolved in favor of the latter.