OBTAINING CO 2 FROM FERMENTATION PROCESS Another source of CO 2 is fermentation industry If yeast is used alcohol and CO 2 are produced Yield of CO 2 varies with mode of fermentation ID: 781470
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Slide1
LECTURE 6
INDUSTRIAL GASES
Slide2OBTAINING CO
2 FROM FERMENTATION PROCESS
Another source of CO
2
is fermentation industry
If yeast is used, alcohol and CO
2
are produced
Yield of CO
2
varies with mode of fermentation
Recovery and purification of CO
2
(from fermentation) requires no cooling (temp nearly 40°C )
So, No special cooling is necessary and CO2 content starts above 99.5%.
Slide3Fermentation CO
2 purification method
3 scrubbers containing stoneware spiral packing;
Weak alcohol solution removes most of the alcohol carried by gas;
next 2 scrubbers use deaerated water (removes water soluble impurities); Potassium di chromate oxidisex the alcohol and aldehyde in the gas and coolsH2SO4 acts as dehydrating agent.Sodium carbonate removes entrained acid in gas; when acid is neutralised, CO2 is releasedOil scurbber contains glycerin; absorbs the oxidsex products and send odorless gas to compressorH2SO4 after use is send to distillery for pH control
Slide4Hydrogen
Important gaseous raw material for chemical and petroleum industries
Sold as gas or liquid
Used in making Ammonia, methanol, etc.
Envisioned as fuel for futureRenewable fuel (Green)
Slide5Manufacturing of Hydrogen
Derived from carbonaceous materials (primarily hydrocarbons) and/or water
Carbonaceous materials or water is decomposed by application of energy which may be
electrical, chemical
or thermalOther methods also exist
Slide6Electrolytic method (Water/Brine)
Produces high purity water (>99.7 % pure)
Passing direct current through an aqueous solution of alkali and decomposing the water i.e.
Electrolysis cell electrolyzes 15% NaOH solution and uses Iron cathode and Nickel plated iron anode, has asbestos diaphragm
Operates around 60 – 70 °C. Produces around 56 L of hydrogen ; 28 L Oxygen ; per Mega JoulePure H2 is suitable for hydrogenating edible oils
Slide7Hydrogen production in microbial electrolysis cell
Slide8Steam-Hydrocarbon Reforming Process
Catalytically reacting a mixture of steam and hydrocarbons at elevated temperatures
Forms a mixture of H
2
and oxides of CLight hydrocarbons are used e.g. CH4
Slide9Reforming Reaction
First reaction is Reforming
Highly endothermic
high T & low P
Excess steam is used
Slide10Shift Reaction
Second reaction is water-gas-shift reaction
Mildly endothermic
Low T
Excess steam used to force reaction to completionCatalyst is used (Fe2O3)
Slide11Steam Reforming
Both reactions occur in Steam Reforming Furnace at Temp
760 – 980 °C.
Composition of product stream depends upon process conditions, including T, P and excess steam, which determine equilibrium and the velocity through the catalyst bed (approach to equilibrium)Product contains app 75% H2, 8%CO, 15% CO2. Remainder N2 and unconverted CH4
Slide12Producing Additional Hydrogen
Water gas shift conversionAdditional steam is used
Temp is reduced to 315 °C – 370 °C
Single stage converts 80 to 95% of residual CO to CO
2 and H2Reaction is exothermic, reaction T rises; enhances the reaction rate but adverse effect on equilibrium
Slide13Shift Conversion
When High Conc of CO exist in feed, shift conversion is conducted in 2 or more stages
Interstage cooling to prevent excessive temp rise
First stage at High T, to obtain high reaction rate
Second stage at low T, to obtain good conversion
Slide14Slide15Hydrogen manufacture – Partial Oxidation Process
Rank next to steam-hydrocarbon process in the amount of Hydrogen made
Use natural gas, refinery gas or other hydrocarbon gas mixtures as feedstock
Benefit– Also accept liquid hydrocarbon feedstocks such as gas oil, diesel oil and heavy fuel oil
Slide16Partial Oxidation Process
Non catalytic partial combustion of the hydrocarbon feed with oxygen in the presence of steam
Combustion chamber temp 1300 and 1500 °C
When methane is used
First reaction is highly exothermic and produces enough heat to sustain the other two reactions
Overall Reaction
Slide17Partial Oxidation Process
For efficient operation, heat recovery using Waste Heat Boilers is important
Product gas composition depends upon the carbon/hydrogen ratio in feed and amount of steam added
Pressure does not have a significant effect and conducted at 2 – 4 MPa.
This permits the use of more compact equipment and reducing compression costs
Slide18Composition of mixture
Process has higher carbon oxides/hydrogen ratio than steam-reformer gas
Slide19Remaining Conversion
Same as for Steam-hydrocarbon reforming processWater gas shift conversion
CO
2
removal via mono/di ethanol amine scrubbingMethanation
Slide20Coal Gasification Process
More emphasis on Coal as feedstock for hydrogen due to diminishing oil and gas resources
Will be discussed later in Coal Gasification
Gases produced require the water-gas shift conversion and subsequent purification to produce high-purity hydrogen.
Slide21Comparison for 4 main process for H
2 manufacture
Slide22Hydrogen Purification
Slide23CO, CO
2 & H2S removal
CO Removal
Water gas shift reactionCO2 & H2S MEA/DEA (mono/di ethanolamime). Chemical ReactionsStripping with steam at 90-120°CCapable of reducing CO
2
conc to < 0.01% by volume
Slide24Disadvantage of ethanolamines
Corrosive nature of ethanolaminesCorrosion most severe at elevated temps and high conc of acid gas in solution
Use of S.S on vulnerable areas
Limiting the conc of ethanolamines in aq solution to limit CO
2 in solution, removing O2 from system and degradation productsUse of corrosion inhibitor
Slide25Hot Potassium Carbonate Process
Similar to Amine treatment
Less purity than amine treatment (CO
2
conc down to 0.1% volume); though more economical for conc down to 1% or greaterHot/Boiling solution absorbs CO2 under pressureSteam consumption is reduced and Heat Exchangers eliminated.Catacarb process mainly important (catalyst)
Slide26Adsorption Purification
Fixed bed adsorption can remove CO
2
, H
2O, CH4, C2H6, CO, Ar and N2 impuritiesThermal and Pressure Swing AdsorptionThermal impurity adsorbed at Low T and desorbed thermally by raising Temp
Pressure Swing Adsorption (PSA) Impurities are adsorbed by molecular sieve under pressure and desorbed at same T but low Pressure
Purge gas may be used to aid desorption
For continuous operation 2 beds are normally employed.
Slide27Advantage of PSA over thermal adsorption
Operate at shorter cycleThereby reduces vessel sizes and adsorbent requirements
Capable of purifying typical hydrogen stream to less than 1 to 2 ppm total impurities (high purity)
Slide28Cryogenic liquid purification
Highly purity >99.99% obtained when hydrogen separated from liquid impurities (N
2
and CO, CH
4)Employed at -180°C; 2.1 MPaFinal purification with activated Carbon, silica gel or molecular sieves
Slide29Oxygen
Slide30Manufacturing
Air separation methods:
Cryogenic process
Pressure swing adsorption process
Electrolysis of waterBy chemical reaction in which oxygen is freed from a chemical compound
Slide31Process Flow Sheet For Oxygen & Nitrogen Production
Slide32The air is compressed to about 94 psi (650 kPa or 6.5 atm) in a multi-stage compressor. It then passes through a water-cooled cooler to condense any water vapor, and the condensed water is removed in a water separator.
The air passes through a molecular sieve adsorber. The adsorber contains zeolite and silica gel-type adsorbents, which trap the carbon dioxide, heavier hydrocarbons, and any remaining traces of water vapor. Periodically the adsorber is cleaned to remove the trapped impurities. This usually requires two adsorbers operating in parallel, so that one can continue to process the air-flow while the other one is flushed
The pretreated air stream is split. A small portion of the air is diverted through a compressor, where its pressure is boosted. It is then cooled and allowed to expand to nearly atmospheric pressure. This expansion rapidly cools the air, which is injected into the cryogenic section to provide the required cold temperatures for operation.
The main stream of air passes through one side of a pair of plate fin heat exchangers operating in series, while very cold oxygen and nitrogen from the cryogenic section pass through the other side. The incoming air stream is cooled, while the oxygen and nitrogen are warmed. In some operations, the air may be cooled by passing it through an expansion valve instead of the second heat exchanger. In either case, the temperature of the air is lowered to the point where the oxygen, which has the highest boiling point, starts to liquefy.
Slide33The air stream—now part liquid and part gas—enters the base of the high-pressure fractionating column. As the air works its way up the column, it loses additional heat. The oxygen continues to liquefy, forming an oxygen-rich mixture in the bottom of the column, while most of the nitrogen and argon flow to the top as a vapor.
The liquid oxygen mixture, called crude liquid oxygen, is drawn out of the bottom of the lower fractionating column and is cooled further in the subcooler. Part of this stream is allowed to expand to nearly atmospheric pressure and is fed into the low-pressure fractionating column. As the crude liquid oxygen works its way down the column, most of the remaining nitrogen and argon separate, leaving 99.5% pure oxygen at the bottom of the column.
Meanwhile, the nitrogen/argon vapor from the top of the high-pressure column is cooled further in the subcooler. The mixed vapor is allowed to expand to nearly atmospheric pressure and is fed into the top of the low-pressure fractionating column. The nitrogen, which has the lowest boiling point, turns to gas first and flows out the top of the column as 99.995% pure nitrogen.
The argon, which has a boiling point between the oxygen and the nitrogen, remains a vapor and begins to sink as the nitrogen boils off. As the argon vapor reaches a point about two-thirds the way down the column, the argon concentration reaches its maximum of about 7-12% and is drawn off into a third fractionating column, where it is further recirculated and refined. The final product is a stream of crude argon containing 93-96% argon, 2-5% oxygen, and the balance nitrogen with traces of other gases.
Slide34Higher Oxygen purity
If higher purity is needed, one or more additional fractionating columns may be added in conjunction with the low-pressure column to further refine the oxygen product. In some cases, the oxygen may also be passed over a catalyst to oxidize any hydrocarbons. This process produces carbon dioxide and water vapor, which are then captured and removed.
If the oxygen is to be liquefied, this process is usually done within the low-pressure fractionating column of the air separation plant. Nitrogen from the top of the low-pressure column is compressed, cooled, and expanded to liquefy the nitrogen. This liquid nitrogen stream is then fed back into the low-pressure column to provide the additional cooling required to liquefy the oxygen as it sinks to the bottom of the column.
Uses
It is one of the life-sustaining elements on Earth and is needed by all animals.
Oxygen and acetylene are combusted together to provide the very high temperatures needed for welding and metal cutting
When oxygen is cooled below -297° F (-183° C), it becomes a pale blue liquid that is used as a rocket fuel.
It is used in blast furnaces to make steel, and is an important component in the production of many synthetic chemicals, including ammonia, alcohols, and various plastics.
Slide37Thank You.