U.S. patent application number 17/585277 was filed with the patent office on 2022-06-09 for oxy-fuel cracking boilers using co2 as the working fluid.
This patent application is currently assigned to LAMAR UNIVERSITY, A COMPONENT OF THE TEXAS STATE UNIVERSITY SYSTEM, AN AGENCY OF THE STATE OF TEXAS. The applicant listed for this patent is Lamar University. Invention is credited to Russel Buss, Daniel H. Chen, Dan P. Fernandes.
Application Number | 20220177389 17/585277 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-09 |
United States Patent
Application |
20220177389 |
Kind Code |
A1 |
Chen; Daniel H. ; et
al. |
June 9, 2022 |
OXY-FUEL CRACKING BOILERS USING CO2 AS THE WORKING FLUID
Abstract
Disclosed is a boiler may that uses recycled carbon dioxide as a
working fluid. Instead of releasing high-purity CO.sub.2 into the
atmosphere, the bulk of the CO.sub.2 is utilized as the working
fluid and the produced CO.sub.2 is captured and sent to a pipeline
for utilization or storage. These systems will minimize heat loss
and achieve essentially zero CO.sub.2 emission to the air.
Inventors: |
Chen; Daniel H.; (Beaumont,
TX) ; Buss; Russel; (Beaumont, TX) ;
Fernandes; Dan P.; (Beaumont, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lamar University |
Beaumont |
TX |
US |
|
|
Assignee: |
LAMAR UNIVERSITY, A COMPONENT OF
THE TEXAS STATE UNIVERSITY SYSTEM, AN AGENCY OF THE STATE OF
TEXAS
Beaumont
TX
|
Appl. No.: |
17/585277 |
Filed: |
January 26, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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17388870 |
Jul 29, 2021 |
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17585277 |
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63058641 |
Jul 30, 2020 |
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International
Class: |
C07C 4/02 20060101
C07C004/02; B01J 6/00 20060101 B01J006/00 |
Claims
1. A method for heat treating hydrocarbons, comprising: providing a
hydrocarbon fuel source mixed with an oxidant source and carbon
dioxide gas to a boiler, wherein the hydrocarbon fuel source is
burned in the boiler to produce a heated outlet gas comprising
carbon dioxide and water; separating the water from the carbon
dioxide in the heated outlet gas; and recycling at least a portion
of the separated carbon dioxide back to the boiler.
2. The method of claim 1, wherein the hydrocarbon fuel source
includes natural gas.
3. The method of claim 1, further comprising heating the recycled
portion of the separated carbon dioxide stream with heat from the
heated outlet gas exiting the boiler.
4. The method of claim 1, further comprising heating at least a
portion of the oxidant source with heat from the heated outlet gas
exiting the boiler.
5. The method of claim 1, further comprising providing the water
separated from the water/carbon dioxide stream back to the boiler,
and heating the water with heat generated in the boiler to produce
high pressure steam.
6. The method of claim 1, further comprising superheating the high
pressure steam with heat from the heated outlet gas exiting the
boiler.
7. The method of claim 1, wherein the water is separated from the
carbon dioxide in one or more mol sieve beds.
8. The method of claim 7, further comprising heating the mol sieve
beds with at least some of the recycled carbon dioxide.
9. The method of claim 7, wherein the one or more mol sieve beds
includes two mol sieve beds.
10. The method of claim 7, wherein the one or more mol sieve beds
adsorb water at 125.degree. C.
11. The method of claim 1, further comprising superheating and
cooling the heated outlet gas before separation.
12. The method of claim 1, further comprising pressurizing the
recycle carbon dioxide before providing to the boiler.
Description
PRIORITY CLAIM
[0001] This patent application is a divisional of U.S. patent
application No. 17/388,870, filed Jul. 29, 2021, which claims
priority to U.S. Provisional Patent Application No. 63/058,641
filed Jul. 30, 2020, each of which is incorporated by reference as
if fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention generally relates to the formation of ethylene
and/or propylene from hydrocarbon feedstocks.
[0004] 2. Description of the Relevant Art
[0005] Ethylene and propylene are major petrochemicals as they are
a primary building block to produce many other chemicals and
products. Ethylene and propylene are produced from a variety of
hydrocarbon feedstocks using cracking or pyrolysis in a furnace
commonly referred to as a "cracker." Common hydrocarbon feedstocks
of steam cracking are the ethane/propane derived from
natural/associated gas, naphtha, and other hydrocarbons.
[0006] Cracking or pyrolysis is a reaction in the gas phase at high
temperatures (e.g., above 800.degree. C. such as 840.degree. C. to
890.degree. C.). During a cracking process, gaseous hydrocarbons
(typically, ethane, or propane) are treated with steam at high
temperatures. Under these conditions the hydrocarbons in the feed
stream are converted into ethylene and/or propylene plus hydrogen
by various free radical or molecular reaction schemes. In a typical
cracking process, the steam to hydrocarbon ratio is 0.3-0.5.
Dilution steam is supplied to the furnace area of the cracker at
elevated temperature and pressure (e.g., 7 bar and 190.degree. C.).
The dilution steam has a dual function of lowering the hydrocarbon
partial pressure and reducing the coking rate in the radiant
coils.
[0007] Temperature along with reactor pressure and
steam-hydrocarbon ratio are the critical parameters in cracking
operations. Cracking can be represented by free radical or
molecular reaction schemes. The COT (coil outlet temperature) is an
important indicator for severity to avoid over or under
cracking.
[0008] Cracking, however, produces large amounts of greenhouse
gases and other pollutants such as NOx. The recently released
report "The Fourth National Climate Assessment" by the U.S.
government on the National Oceanic and Atmospheric Administration
website highlights that climate change is real and global warming
will increase in the future which will threaten the health and
wellbeing of the world populations. Global warming will further
increase the economic costs to countries due to an increasing
number of natural disasters in the future.
[0009] The rise in the global emissions of carbon dioxide was at
2.7 percent in 2018. This expected increase, would bring fossil
fuel and industrial emissions to a record high of 37.1 billion tons
of carbon dioxide per year. The US, China, and India will account
for 2.5 percent, 5 percent, and 6 percent growth of emissions
respectively.
[0010] According to the UN-backed scientific panel, nations have
barely a decade left to take unprecedented actions to cut emissions
in half by 2030 to keep the Earth's warming below 1.5 degrees
Celsius or suffer the consequences of climate change. A global
economy which is growing at a fast pace coupled with the
accelerated development in nations like China and India, which are
heavily reliant on coal for power production, will inevitably stoke
more global emissions of carbon dioxide. Coal accounts for 60
percent of electricity production in China. The availability of
cheap feedstock of natural gas in the U.S., will warrant the
construction of ethane crackers in the U.S. According to the
American Chemistry Council, $200 billion will be invested on new
ethane cracker facilities to take advantage of the cheap
availability of natural gas in the U.S.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Advantages of the present invention will become apparent to
those skilled in the art with the benefit of the following detailed
description of embodiments and upon reference to the accompanying
drawings in which:
[0012] FIGS. 1A and 1B depict a process flow diagram for an
ethylene and/or propylene cracker unit, according to some
embodiments.
[0013] FIG. 2 depicts a process flow diagram for an ethylene and/or
propylene cracker unit employing two molecular sieve packed beds,
according to some embodiments.
[0014] FIG. 3 depicts a process flow diagram for a boiler unit,
according to some embodiments.
[0015] FIG. 4 depicts a process flow diagram for a boiler unit
employing two molecular sieve packed beds, according to some
embodiments.
[0016] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings and will herein be described in
detail. It should be understood, however, that the drawings and
detailed description thereto are not intended to limit the
invention to the particular form disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the present
invention as defined by the appended claims. Note, the headings are
for organizational purposes only and are not meant to be used to
limit or interpret the description or claims.
DETAILED DESCRIPTION
[0017] It is to be understood the present invention is not limited
to particular devices or methods, which may, of course, vary. It is
also to be understood that the terminology used herein is for the
purpose of describing particular embodiments only, and is not
intended to be limiting. As used in this specification and the
appended claims, the singular forms "a", "an", and "the" include
singular and plural referents unless the content clearly dictates
otherwise. Furthermore, the word "may" is used throughout this
application in a permissive sense (i.e., having the potential to,
being able to), not in a mandatory sense (i.e., must). The term
"include," and derivations thereof, mean "including, but not
limited to." The term "coupled" means directly or indirectly
connected.
[0018] Furnace with CO.sub.2 Recycle
[0019] FIGS. 1A and 1B depict a process flow diagram for an
ethylene and/or propylene cracker unit, according to some
embodiments. Cracker unit 100 may work as a convection furnace,
like a steam boiler. Cracker unit 100 may be, for example, a
radiant coil cracker unit. In the illustrated embodiment, natural
gas 102 and oxygen 104 are provided through compressors 106 to
combustion chamber 108. Oxy-fuel combustion occurs in combustion
chamber 108 to produce heated CO.sub.2 gas stream 110, which
supplies the heat for the cracking reaction in cracker unit
100.
[0020] In various embodiments, after cracking is finished, carbon
dioxide 112 is recycled to the combustion chamber 108. Thus,
instead of releasing high-purity CO.sub.2 into the atmosphere, the
CO.sub.2 is retained in the system and utilized as the working
fluid. In the illustrated embodiment, an ethylene cracker or boiler
utilizes regenerative or other heat exchange media and recycled hot
CO.sub.2 to minimize heat loss and to achieve substantially zero
CO.sub.2 emission to the air. The hot cracked gas product stream
(gaseous ethylene and/or propylene) may be used to heat up the
ceramic media or other heat exchange media and to serve as the
quench step for the furnace/boiler effluent.
[0021] Various typical operating conditions of the illustrated
embodiment are described as follows. Piped natural gas 102 at 2 bar
is supplied to combustion chamber 108 (shell side of ethane
cracker) at 250.degree. C. Oxygen 104 from an air separation unit
(ASU) at 99.4% purity is supplied at 2 bar and 200.degree. C. In
the presence of circulated carbon dioxide 112 at 2 bar and
550.degree. C., natural gas 102 is combusted with oxygen 104 in
combustion chamber 108. The products of combustion are water and
carbon dioxide 110. The recycled carbon dioxide is added to
maintain the adiabatic flame temperature in an acceptable range.
The heat of combustion is transferred to cracker unit 100. In
cracker unit 100, ethane and steam mixture 114 is flowing through
the coils at an s/c ratio of about 0.4. In a specific embodiment,
the coil reactor has 48 tubes with a length of 10.5 m and an inner
diameter of 0.085 m for each tube. Other configurations and
dimensions are possible, depending on the amount of material being
processed. In the illustrated embodiment, the maximum operating
pressure is 2 bar. Cracked gas 116 leaving cracker unit 100 has the
COT at 856.degree. C. and a pressure of 2 bar. The ethylene
produced is about 52% by weight. The cracked gas 116 heats up the
saturated steam to superheated steam in superheater 122, which is
then fed into steam turbine 126 to generate lower pressure steam
128 at 2 bar. In some embodiments, the cracked gas 116 exits the
process and is provided to a quench tower at 117. The power
generated by steam turbine 126 is, in one embodiment, 0.67 MW,
which is sufficient to power at least some of the equipment of the
plant (e.g., using electric generator 130). In some embodiments,
low-pressure steam 128 is combined with hydrocarbon feed 132 (e.g.,
ethane) at mix valve 134 and the resulting mixture fed to cracker
unit 100 as ethane and steam mixture 114. The remaining
low-pressure steam 128 can be used in the plant for steam tracing
of lines or exported elsewhere at valve 136.
[0022] In certain embodiments, after giving the heat for the
endothermic reaction to cracker unit 100, combusted gas 138 from
the cracker unit is fed to a double-bed ceramic heat exchanger
media 140 by split valve 143. The double-bed ceramic heat exchange
includes first heat exchange 140A in a regenerative mode and second
heat exchanger 140B in a heating mode. The double-bed ceramic heat
exchanger 140 is used to preheat the incoming CO.sub.2 142 (which
is split by valve 143) from the CO.sub.2 compressor 144 before the
CO.sub.2 is fed to the combustion chamber 108 as circulated carbon
dioxide 112 through valve 145. The combusted gas stream 146 may
leave the double-bed ceramic heat exchanger 140 through valve 147
to further exchange heat with water 118 in steam boiler 148 to
generate high pressure steam and heats up the ethane and steam mix
in another heat exchanger from 150 to 300.degree. C.
[0023] The combusted gas stream 146 is then fed to separator 120
(e.g., at atmospheric pressure and temperature) where water 118 is
separated from carbon dioxide 152. Separator 120 may be, for
example, a knockout drum or condenser. The water 118 from the
separator 120 is fed to boiler feed water pump 154, which pumps it
at a high pressure (e.g., 100-150 bar) to the steam boiler 148.
Extra high pressure steam can be generated by feeding water from a
deaerator 155 via the pumps 154 to the HP boilers to generate
steam. The carbon dioxide 152 is compressed in CO.sub.2 compressor
144 to 2 bar and a temperature of 100.degree. C. 97% of this high
purity CO.sub.2 is recycled back to cracker unit 100 as CO.sub.2
142, the remaining 3% CO.sub.2 154 (e.g., 3 tons/hour) must be
purged to maintain the mass balance of the system. This carbon
dioxide 154 can be compressed to above 74 bar pressure and cooled
to .about.32.degree. C. to be in a supercritical state for export
in pipelines to EOR/ sequestration. The method of ethylene
production in ethane crackers by recycling CO.sub.2, shown in FIGS.
1A and 1B, minimizes carbon emission compared to conventional
cracking processes.
[0024] Alternative Embodiments with Molecular Sieve Packed Beds
[0025] In various embodiments, a solid desiccant may be used to
remove water at elevated temperatures and warmer CO.sub.2 is
recycled back to the combustion chamber. FIG. 2 depicts a process
flow diagram for an ethylene and/or propylene cracker unit
employing two molecular sieve packed beds, according to some
embodiments. In the illustrated embodiment, two beds 200 are
implemented in the process to adsorb water at 125.degree. C. The
warmer dry CO.sub.2 112 may then be recycled through a series of
heat exchangers 202 back to combustion chamber 108.
[0026] In some embodiments, the saturated molecular sieve beds 200
are regenerated by slip stream 204 (.about.10%) of the dry CO.sub.2
at 315.degree. C. coming from regenerating CO.sub.2 heater 206.
Then, after heat integration in heater 208 (e.g., to heat up oxygen
or natural gas fuel to the combustor), the water in the cooled slip
stream (e.g., cooled by cooler 210) is removed in separator 212
(e.g., a knockout drum or condenser) at ambient temperatures. The
dry slip stream 214 is fed back to join the main combustion exhaust
stream right before the adsorption molecular sieve bed 200, as
shown in FIG. 2. In various embodiments, ethane and steam mixture
114 (e.g., feed for cracker unit 100) is generated by mixing steam
from steam generator 214 and hot ethane after passing ethane heater
216.
[0027] In the illustrated embodiment, the energy saving (natural
gas needed for oxy-combustion) can be estimated as the enthalpy
difference between 125.degree. C. and 35.degree. C. (.about.83
kJ/kg) for 90% of the wet CO.sub.2 stream that is recycled back to
the combustion chamber. Note that the fraction of the dry CO.sub.2
sent to the pipeline is relatively small compared to recycle
CO.sub.2 (.about.3%:97%). The energy penalty for compression
CO.sub.2 for 0.3 bar pressure drop (based on 4A Mol Sieve Grace,
4-8 mesh beads) across the packed beds is estimated to be .about.32
kJ/kg with 70% adiabatic efficiency. So the benefits outweighs the
penalty for this arrangement.
[0028] It should also be noted that the configuration shown in FIG.
2 may further be optimized in terms of the desiccant used,
adsorption/regeneration temperatures, and pressure drops across the
packed beds. The packed beds may have other contemplated
embodiments as well. For instance, a 2+1 bed vessel arrangement (2
vessels are running while 1 vessel is regenerating) may be
implemented instead of the 1+1 vessel arrangement shown in FIG.
2.
[0029] Boiler with CO.sub.2 Recycle
[0030] Principles from the cracker unit of FIGS. 1A and 1B may also
be applied to a boiler operation by replacing the cracker section
with a boiler. FIG. 3 depicts a process flow diagram for a boiler
unit, according to some embodiments. In the illustrated embodiment,
natural gas 102 is fed to boiler drum 300. In some embodiments,
natural gas 102 is mixed with hot oxygen 302 and hot CO.sub.2
recycle 304 for combustion in the boiler burner. Hot water 306 may
also be fed to boiler with high pressure saturated steam 308
exiting the boiler. Exhaust 310 from boiler 300 may be fed to
heater 312, which heats water feed 314 to hot water 306. Water feed
314 may include water recycle 316 and/or make up water 318 stored
in water drum /deaerator 320 and fed by pump 322.
[0031] Exhaust 310 may pass through heater 312 to superheater 324.
Superheater 324 heats high pressure steam 308 to form superheated
high pressure steam 326. Exhaust 310 may then pass to CO.sub.2
heater 328, which heats recycled CO.sub.2 330 to hot CO.sub.2
recycle 304. Exhaust 310 then passes to oxygen heater 332, which
heats oxygen 104 to hot oxygen 302. Exhaust then enters separator
334 (e.g., a knockout drum or condenser) to generate water recycle
316 and CO.sub.2 336. CO.sub.2 336 is then fed to compressor 338
and then is recycled or sent for enhanced oil recovery,
sequestering, or export at valve 340.
[0032] Alternative Embodiments with Molecular Sieve Packed Beds
[0033] As with the cracker unit, various embodiments may be
contemplated with a solid desiccant being used to remove water at
elevated temperatures and warmer CO.sub.2 is recycled back to the
boiler. The solid desiccant may include, for example, a molecular
sieve, silica gel, and activated alumina to dehydrate the water
containing CO.sub.2 stream at elevated temperatures in lieu of a
condenser operated at ambient temperatures. FIG. 4 depicts a
process flow diagram for a boiler unit employing two molecular
sieve packed beds, according to some embodiments. In the
illustrated embodiment, two beds 400 are implemented in the process
to adsorb water at 125.degree. C. The warmer dry CO.sub.2 may then
be recycled through compressor 402, oxygen heater 403, and heater
404 back to boiler 300 as hot CO.sub.2 304. Oxygen heater 403 heats
oxygen 104 to hot oxygen 302 for boiler 300.
[0034] Exhaust 310 goes through superheater 324 and recycle
CO.sub.2 heater 404 before entering regenerating CO.sub.2 heater
406 and water heater 408. Exit feed 410 from beds 400 passes
through natural gas heater 412 and then to cooler 414. The exit
feed 410 then goes to separator 416 (e.g., a knockout drum or
condenser) that produces water 418 and CO.sub.2 recycle 420.
CO.sub.2 recycle 420 may be pressurized by compressor 422 and sent
back to combine with the feed for beds 400. A slip stream
(.about.10% of the dry CO.sub.2) is first heated by regenerating
CO.sub.2 heater 406, then is used to regenerate a mol sieve bed
400, the wet effluent 410 then passes through the natural gas
heater 412 to pre-heat the natural gas stream 102 to the combustor.
The wet CO.sub.2 stream then is then cooled off by an air cooler
414 before entering the knockout drum 416. The cold dry CO.sub.2
420 passes through a compressor 422 before rejoining the combustion
exhaust gas (CEG) stream.
[0035] Again, the energy saving for the boiler may be estimated as
the enthalpy change from 35.degree. C. to 125.degree. C. (.about.83
kJ/kg) for 90% of the wet CO.sub.2 stream that is recycled back to
the boiler. Note that the fraction of the dry CO.sub.2 sent to the
pipeline is relatively small compared to recycle CO.sub.2
(.about.3%:97%). The energy penalty for compression of CO.sub.2 for
0.3 bar pressure drop across the packed beds may be estimated to be
.about.32 kJ/kg with 70% adiabatic efficiency. Therefore, the
benefit outweighs the penalty for this arrangement, as with the
arrangement in FIG. 2. Additional optimizations, such as those
described with respect to FIG. 2, may be added to FIG. 4.
[0036] Improvements Over the Existing Methods
[0037] Current steam cracking furnaces all emit CO.sub.2 and NOx to
the atmosphere. The recycled CO.sub.2 furnaces are operated at the
same pressure of cracking which takes place in the coils of the
cracker. Further, using pure oxygen as the oxidizer in furnaces
results in no nitrogen oxides (NOx) emission. The net CO.sub.2
exported is of high-purity pipeline grade. Some advantages include:
[0038] (1) The application of circulating CO.sub.2 concept to
ethane/propane cracking furnaces to produce ethylene/propylene
reduces CO.sub.2 emissions. [0039] (2) At the same time,
integrating the furnace exhaust heat for preheating, steam
generation, or power generation (running a turbine) reduces energy
consumption of the cracking system. [0040] (3) At the minimum
natural gas (NG) consumption, the cracking system will have the
lowest carbon footprint. [0041] (4) The same circulating CO.sub.2
concept can be extended to steam boiler to generate steam with
CO.sub.2 production for EOR or other CO.sub.2 utilization purposes
(e.g., urea, baking soda, or polycarbonate). [0042] (5) A
facility-wide CO.sub.2 pipeline network to deliver CO.sub.2 as a
working gas for major combustion units such as furnaces, boilers,
and heaters without greenhouse and NOx emissions.
[0043] Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as examples of
embodiments. Elements and materials may be substituted for those
illustrated and described herein, parts and processes may be
reversed, and certain features of the invention may be utilized
independently, all as would be apparent to one skilled in the art
after having the benefit of this description of the invention.
Changes may be made in the elements described herein without
departing from the spirit and scope of the invention as described
in the following claims.
* * * * *