SYSTEM AND METHOD FOR PRODUCING AMMONIA, UREA, AND UAN

A fertilizer production plant is co-located with an ethanol production plant. Low value organic material waste such as corn fiber is gasified to produce hydrogen. Ambient air is separated to produce nitrogen and oxygen. Hydrogen and nitrogen are reacted to produce ammonia. Carbon dioxide generated by the ethanol production plant and the ammonia are reacted to produce urea. The oxygen and ammonia are used to produce ammonium nitrate, and urea and ammonium nitrate are processed to produce area ammonium nitrate (UAN).

BACKGROUND

Over the past two decades, production of ethanol fuel has grown dramatically, and the United States became the world's largest ethanol producer. Ethanol distillery plants are located in more than half of the states of the United States. Most ethanol produced in the United States comes from corn.

Corn fiber is a low-value stream byproduct that is produced by ethanol plants. Currently this corn fiber stream is combined with protein streams to produce DDGS (Dried Distillers' Grain with Solubles), which is sold to cattle markets. A current trend in the ethanol industry involves separation of the protein from the DDGS to produce a higher value product.

The problem with this approach involves the value of the corn fiber that is left after protein has been removed from DDGS. The resulting lower protein corn fiber stream has very little market value and has proven to be difficult to sell. This negatively affects the overall value of the protein separation process, because the net market value of the two resulting products (high protein feed and low protein corn fiber) is less than the net market value of the original DDGS product.

In addition, the ethanol plant produces excess carbon dioxide, which currently is vented to the atmosphere. Any value the carbon dioxide has is lost, and adding carbon dioxide to the atmosphere has negative ecological effects on the environment.

SUMMARY

A fertilizer production plant is co-located at an ethanol production plant. Organic material waste (such as corn fiber) and carbon dioxide generated by the ethanol production plant and ambient air are used to produce agricultural fertilizer such as anhydrous ammonia, aqueous ammonia, dried urea, and urea ammonium nitrate (UAN).

DETAILED DESCRIPTION

Co-Located Ethanol Plant and Fertilizer Plant

FIG.1is a block diagram includes ethanol plant10, fertilizer production system12, and corn fiber storage bins14which are located so that corn fiber and carbon dioxide (CO2) produced during the ethanol production from ethanol plant10can be used by system12to produce fertilizer products. The fertilizer products that can be produced include anhydrous ammonia product, aqueous ammonia product, urea product, and urea ammonium nitrate (UAN) product.

Ethanol plant10supplies warm water, corn fiber, and CO2 to fertilizer production system12. Ambient (atmospheric) air is also an input to system12. Hot water is returned to the ethanol plant10. Ash and burner exhaust produced in gasification of the corn fiber can be returned to plant10for disposal or can be scrubbed and disposed of by fertilize production system12. Natural gas is also supplied for drying the urea product, and a vent stack is provided for removal of moisture and carbon monoxide from the urea dryer.

The manufacture of agricultural fertilizer (such as ammonia, urea, and urea-ammonium-nitrate products) is performed onsite at ethanol plant10. Fertilizer production process12uses low-value feedstock produced during ethanol production. The low-value feedstock includes corn fiber left over after protein is extracted from the dried distiller's grains, carbon dioxide produced as a by-product of ethanol manufacturing, nitrogen from ambient air, and heat recovered from the exothermic reactions during the creation of ammonia, urea, or UAN products. This fertilizer production process can operate continuously or in batches, and can produce one, two, or all three of the fertilizer products simultaneously.

The entire manufacturing process and storage of the end products ammonia, urea, or UAN is completed onsite at ethanol plant10. Ammonia, urea, and UAN products can then be sold as-is to various markets. The agricultural market is a primary market, given that these forms of ammonia, urea, and UAN are the same forms of nitrogen fertilizer currently used in agriculture.

Low-value feedstocks provide price-stability and predictability to the market for these fertilizer end products. Inbound shipping costs of feedstocks are eliminated because the feedstocks are already onsite at the ethanol plants. Substantially reduced outbound costs of the fertilizer products are realized in the agricultural market because these three fertilizer end products can be shipped directly from a local ethanol plant to local farms. Reduced environmental emissions are realized due to less carbon dioxide and carbon monoxide being released to the atmosphere, and less fossil fuel is needed at the ethanol plant due to recovery of heat from the exothermic reactions occurring during the fertilizer production process.

Fertilizer production plant12is located next to ethanol plant10. Dried corn fiber and clean CO2 are provided by ethanol plant. The corn fiber is delivered from ethanol plant10to storage bins14, from which the corn fiber can be supplied on demand to fertilizer production system12. CO2 can be sent directly from the ethanol plant with no surge capacity provided. Any interruption in CO2 due to upsets at the ethanol plant will cause an interruption in production of urea.

Utilities such as cleaning solutions, compressed instrument air, steam and cooling tower water can be provided by ethanol plant10. This integration and shared utilities reduces the capital expense required for the installation and operation of the fertilizer production system12.

Ammonia Production

FIG.2is a flow diagram of fertilizer production plant12for production of ammonia products (anhydrous ammonia and aqueous ammonia). Fertilizer production plant12includes gasifier30, pressure swing adsorption (PSA) separator32, liquid scrubber34, hydrogen purifier36, and ammonia reactor38.FIG.2Aalso shows the following flow streams: corn fiber stream40, syngas (synthesis gas) stream42, ash stream44, burner exhaust stream46, warm water stream48, hot water stream50, clean gas stream52, hydrogen product stream54, waste hydrogen56, air stream58, waste nitrogen stream60, nitrogen product stream62, anhydrous ammonia product stream64, and aqueous ammonia product stream66.

Fertilizer production begins with pulling corn fiber from storage bins14to feed gasifier system30. Corn fiber stream40is finely ground corn fiber at 10% moisture. Gasifier30includes an enclosed conveyor that transfers corn fiber stream40through a heated zone that is run at 1200° F. The heated zone will be kept low in oxygen where synthesis gas (syngas), carbon monoxide and hydrogen, are driven off the solids (corn fiber).

Water is added to allow the carbon monoxide to be converted to carbon dioxide and hydrogen to maximize the production of hydrogen.

Nitrogen is produced from atmospheric air. Air will be compressed to 5 psig, filtered and then cooled to 100 F before being sent to a series of PSA separators that will be used to selectively produce a high purity nitrogen stream. Gasifier30will be run inefficiently to allow for the production of high quality nitrogen allowing more nitrogen to leave with the off gas stream.

Nitrogen is produced at high quality and low pressure. This gas is fed to a compressor at ammonia reactor38, where it is heated and then fed to catalyst beds along with compressed hydrogen.

Waste nitrogen stream60from nitrogen purifier32will be sent through gasifier30to push the syngas stream42through the system. Syngas produced in the heated zone will exit the gasifier30and will be passed through liquid scrubber34where ash and tar will be removed from the syngas leaving mostly clean syngas consisting of hydrogen and carbon dioxide.

Water from the bottom of liquid scrubber34is cooled through a recirculation cooler and sent back to the top of the liquid scrubber34. Cool water will cool and condense the tars in syngas stream42, capturing these materials, and capturing any solids materials present in the crude syngas stream. A portion of the water will be blown down to allow for the removal of these captured components. The dirty water stream will be sent to ethanol plant10to be incorporated into the plant evaporation system and leaving the plant as part of the DDGS feed. Clean cool syngas is fed to a compressor and passed through PSA system32where hydrogen is selectively removed from the gas stream.

PSA separator32can be run inefficiently, producing a cleaner hydrogen product, and allowing some hydrogen to leave the system in the waste off gas. Waste off gas will be sent to the burner used to provide heat to gasifier30or to the boiler of ethanol plant10, where the gas will be used to reduce the amount of natural gas used in the ethanol distillation process.

High quality hydrogen stream54from hydrogen purifier36and high quality nitrogen stream62from PSA separator32are fed directly to the ammonia reactor38where it will be compressed, heated and sent through the catalyst beds. Hydrogen and nitrogen stream are fed to catalyst bed reactors that will contain catalysts and will be run at 850° F. and 3600 psig. Each pass through the catalyst bed will partially convert the syngas to ammonia which will require a separation process where Ammonia is separated from the unreacted syngas, and the syngas is recycled back to the reactor or sent to another reactor in series. In this example, the ammonia process is the Haber-Bosch process. An example of the catalyst is ruthenium-calcium-aluminum metal catalyst. In the event the ammonia system does not require as much hydrogen as produced by the gasifier30and PSA gas separator32, excess hydrogen will be vented to the burner on gasifier30.

Residual solids from the gasifier30will leave system20as dry ash stream44that will be cooled, collected and landfilled. It may be possible to sell this product as a fertilizer.

Urea Production

FIG.3is a flow diagram of fertilizer production system20configured for production of urea product. In this configuration, system20includes gasifier30, PSA separator, liquid scrubber34, hydrogen purifier36, and ammonia reactor38as well as flow streams40,42,44,46,48,50,52,54,56,58,60, and62as shown inFIG.2. In addition, flow diagram includes CO2 scrubber70, urea reactor72, urea dryer74, natural gas stream76, stack vent78, urea product80, CO2 feed stream82, CO2 product stream84, ammonia product stream86, and urea product stream88.

Urea production involves reacting CO2 from CO2 product stream84and ammonia product stream in urea processor72at 3600 psig and 400 F. Unreacted CO2 and ammonia are recovered, compressed and returned to urea reactor72.

Urea product stream88is recovered in the form of a 70% solution of urea, which is evaporated to a molten form of urea at 270 F. This molten urea is fed to urea dryer74that sprays and cools the molten urea to produce small particle dried urea. The urea particles can be in the form of prills. Alternatively, it can be in the form of diesel exhaust fluid.

UAN Production