Patent Application
20100132548
The systems and processes disclosed herein relate generally to temperature controlled adsorption for use in dehydrating water rich streams. One particular example relates to the dehydration of fermientation beer for use in producing motor fuel grade ethanol.
Adiabatic adsorption is a process that is employed for bulk water removal, within certain water concentration limits, and purification applications. For example, adiabatic adsorption via molecular sieves is a widely practiced method for removing water from process streams.
The adsorption and desorption reactions that occur during adiabatic adsorption are considered adiabatic since the adsorber and process fluid being treated constitute a system that does not exchange beat with any other adjacent stream within the adsorbent containing contactor. The dynamic nature of the adiabatic water adsorption process, specifically, temperatures rising during adsorption and falling during regeneration, necessarily reduces the adsorbent absolute and differential loading potentials, the latter due to less than perfect regeneration. Additionally, adiabatic operation of an adsorber results in a thermal front preceding the adsorption front. As a consequence, achievable product purities are lowered. For bulk water removal applications, this imposes an upper limit on the water concentration of the process fluid to be treated. The upper limit on water concentration results because in adiabatic adsorption systems, which do not have heat removal capability, the heat liberation associated with a high water content stream feeding an adiabatic adsorber can drive the product end of the bed to a sufficiently high temperature to reduce, or even eliminate, the driving force for adsorption.
As a result, processes for removing water from a mixture containing water and an organic compound to be dehydrated, such as, for example, ethanol, commonly involve process steps to remove water from the mixture prior to the mixture undergoing adsorption.
For example, motor fuel grade ethanol (MFGE) consumer product specifications typically limit water concentrations to less than 1% by volume, and in many countries less than 0.5% by volume. Fuel ethanol (E-95) quality for use in the USA is governed by the specifications listed in ASTM D 4806, entitled “Standard Specification for Denatured Fuel Ethanol for Blending with Gasoline's for use as an Automotive Spark-Ignition Engine Fuel.” The ASTM specification is a water content of 1% by volume. Because ethanol is hygroscopic and easily picks up water from ambient air and the distribution system, the MFGE process specification for water content of the MFGE product is typically tighter than the ASTM specification, and, in at least some instances, can require a maximum water content of about 0.5% by weight. It should be noted that a product stream having about 99% by volume ethanol and about 1% by volume water has about 98.75% by weight ethanol and 1.25% by weight water.
Industrial processes for producing motor fuel grade ethanol (MFGE) include fermentation of starches and lignocellulose. The effluent from the fermentation process, commonly known as fermentation beer, is a water-rich mixture containing water, alcohols, soluble solids, and insoluble solids. The alcohol content of fermentation beer is primarily ethanol. Beer from fermentation typically has a very high water content, which can be in the range of about 70% by weight to about 90% percent by weight of the fermentation beer. The ethanol content of fermentation beer is dependent on the sugar source. For example, fermentation beer for producing ethanol from corn starch can typically have an ethanol content in the range of about 5% to about 15% by weight, such as an ethanol content of about 10% by weight of the fermentation beer. Generally, the ethanol content of fermentation beer is in the range of from about 3% by weight to about 20% by weight. Accordingly, concentrating and purifying the ethanol contained in fermentation beer too achieve an MFGE product that meets specifications entails removing the relatively large amount of water.
Separating ethanol from beer is usually accomplished through distillation up to the ethanol-water azeotropic mixture concentration, which is about 95% by weight ethanol, and subsequent drying via other means in order to meet the MFGE water specification. The distillation sequence generally involves separating solids and some water from the effluent stream of a fermentation process, such as through the use of a beer column or other suitable solids separation unit. The process stream from a solids separation unit, containing nominally from about 55% by weight to about 70% by weight ethanol is sent to a second distillation tower, also known as a Rectifier column, to obtain an ethanol-water overhead product near the ethanol-water azeotropic mixture concentration.
Dehydration of the ethanol-water overhead product can then be accomplished via pressure swing molecular sieve adsorption (PSA), or via other processes such as extractive distillation. The pressure swing molecular sieve adsorption (PSA) technology commonly used to dehydrate the ethanol-water overhead product is an adiabatic process, which is the reason that distillation is normally used to minimize the water in the ethanol-water mixture that feeds the PSA unit.
Systems and processes disclosed herein relate generally to temperature controlled adsorption for use in dehydrating water rich streams. One particular example relates to the dehydration of fermentation beer for use in producing motor fuel grade ethanol (MFGE).
In one aspect, a process for dehydration of a water rich stream is provided that includes providing a process stream to a first temperature controlled adsorber that is undergoing adsorption, where the first temperature controlled adsorber has one or more adsorption flow passages containing an adsorptive material coating and one or more heat transfer flow passages and producing a dehydrated effluent stream. The process stream is passed through the one or more adsorption flow passages, where water is adsorbed by the adsorptive material coating, and a heat of adsorption is generated. The heat of adsorption is removed by passing a cooling fluid through the one or more heat transfer flow passages. The process can further include providing a second temperature controlled adsorber undergoing regeneration that is isolated from the process stream, where the second temperature controlled adsorber has one or more adsorption flow passages containing an adsorptive material coating and one or more heat transfer flow passages, and producing a cooled heating fluid and an effluent stream that is water rich. The heating fluid is provided to the one or more heat transfer flow passages of the second temperature controlled adsorber, and the adsorptive material coating is regenerated by removing water.
In another aspect, a process for production of motor fuel grade ethanol is provided that includes providing a process stream to a first temperature controlled adsorber that is undergoing adsorption, where the first temperature controlled adsorber has one or more adsorption flow passages containing an adsorptive material coating and one or more heat transfer flow passages, and producing an MFGE product stream containing less than 5% by weight water. The process includes passing the process stream through the one or more adsorption flow passages, where water is adsorbed by the adsorptive material coating, generating heat of adsorption, and removing heat of adsorption by passing a cooling fluid through the one or more heat transfer flow passages. The process can further include providing a second temperature controlled adsorber undergoing regeneration that is isolated from the process stream, where the second temperature controlled adsorber has one or more adsorption flow passages containing an adsorptive material coating and one or more heat transfer flow passages, and producing a cooled heating fluid and a water effluent stream. The heating fluid is provided to the one or more heat transfer flow passages of the second temperature controlled adsorber, and the adsorptive material coating is regenerated by removing water.
As used herein, the terms “stream” and “fluid” should be understood as encompassing either liquid or vapor, or both, as suitable based upon the temperature and pressure of the stream or fluid as suitable for the intended application.
Specific examples have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification.
a is a perspective view of a temperature controlled adsorber that can be used in the process of
b is a close-up view of a portion of
c is a close-up view of another portion of
The systems and processes disclosed herein relate generally to temperature controlled adsorption for use in dehydrating water rich streams.
a through 2d illustrate one example of a temperature controlled adsorber 40, which can be utilized in the process of
A wash-coating process can comprise a step of heating a component to be coated, a step of contacting the surface of the component with a slurry comprising an adsorbent and a binder to form an adsorptive material coating 46, and a step of hardening the adsorptive material coating 46. For some applications, the step of contacting may comprise dipping the surface into the slurry or spraying the surface with the slurry.
The adsorptive material coating 46 may have an adsorptive coating thickness 77 (see
As illustrated in
The adsorption layer 50 may provide an adsorption flow passage 53 through the adsorption heat exchanger 40. The adsorption flow passage 53 may be in a direction parallel to an adsorption flow line 54. The heat transfer layer 51 may define a heat transfer flow passage 55 through the adsorption heat exchanger 40. The heat transfer flow passage 55 may be in a direction parallel to a heat transfer flow line 56. The adsorption flow line 54 may be about 90° from the heat transfer flow line 56. This type of system provides cross flow heat exchange. In alternative examples, an adsorption heat exchanger can operate with either parallel or counter flow heat transfer.
As depicted in
The adsorption zone fins 58 may be positioned about perpendicular to the separator plates 52 and may extend about parallel to the adsorption flow line 54. The adsorption zone fins 58 may direct the flow of an adsorbate rich stream 60, as shown in
The adsorption zone contact portions 59 may be positioned about parallel to and in contact with the separator plates 52. The adsorption zone contact portions 59 may be brazed to an adsorption zone facing side 62 of the separator plates 52. The adsorption zone contact portions 59 may provide a support for at least a portion of the adsorptive material coating 46, as depicted in
For some applications, in lieu of the adsorption zone corrugated sheet 57, the adsorption layer 50 may comprise a plurality of adsorption zone fins 58 brazed directly to the separator plates 52. The adsorption zone fins 58 of the adsorption layer 50 may increase the surface area available for adsorptive material coating 46, thereby enhancing the adsorption/desorption efficiency of the adsorption heat exchanger 40.
The adsorption layer 50 may include two adsorption zone header bars 65, as depicted in
The adsorption zone corrugated sheet 57, the adsorption zone fin 58, the adsorption zone contact portion 59 and adsorption zone header bar 65 each may comprise a material, such as but not limited to, aluminized Mylar®, a polymer composite, or a metal. Mylar® is a polyester film produced by E.I. Du Pont De Nemours and Company. Useful metals may include aluminum, copper, titanium, brass, stainless steel, other light metals and alloys with high conductivity, and graphite fiber composite materials. Components of the adsorption layer 50 may provide support for the adsorptive material coating 46.
The adsorptive material coating 46 of the adsorption layer 50 may define the adsorption flow passage 53, as depicted in
The heat transfer layer 51 may include a heat transfer zone corrugated sheet 66, as depicted in
The heat transfer zone fins 67 may be positioned about perpendicular to the separator plates 52 and may extend about parallel to the heat transfer flow line 56. The heat transfer zone fins 67 may direct the flow of heat transfer fluid 69, as shown in
The heat transfer zone contact portions 68 may be positioned about parallel to and in contact with the separator plates 52. The heat transfer zone contact portions 68 may be brazed to a heat transfer zone facing side 72 of the separator plates 52. The heat transfer contact portion width 73 may vary and may depend on the desired density of the heat transfer zone fins 67. The heat transfer contact portion width 73 may be inversely proportion to the density of the heat transfer zone fins 67.
For some applications, in lieu of the heat transfer zone corrugated sheet 66, the heat transfer layer 51 may comprise a plurality of heat transfer zone fins 67 brazed directly to the separator plates 52.
The heat transfer layer 51 may include two heat transfer zone header bars 74, as depicted in
The heat transfer zone corrugated sheet 66, the heat transfer zone fin 67, the heat transfer zone contact portion 68 and heat transfer zone header bar 74 each may comprise any suitable material, such as but not limited to, aluminized Mylar®, a polymer composite, or a metal. Useful metals may include aluminum, copper, titanium, brass, stainless steel, other light metals and alloys with high conductivity, and graphite fiber composite materials.
The separator plate 52 of the adsorption heat exchanger 40 may comprise a sheet material structure, as depicted in
The adsorption heat exchanger 40 further may comprise two side plates 76, as depicted in
Referring back to
When first temperature controlled adsorber 12 is undergoing adsorption, process stream 20 is provided to one or more inlets of first temperature controlled adsorber 12. The process stream 20 can be a vapor stream derived from a reaction process effluent stream. The process stream 20 can also be a water rich stream, and can contain water in an amount of up to about 85% by weight or greater. Process stream 20 flows through the one or more adsorption flow passages 16 of the first temperature controlled adsorber 12. Water is adsorbed by the adsorptive material coating in the one or more adsorption flow passages 16. In one example, the adsorptive material coating contains a polymer and a zeolite, such as, for example, a Type 4A or a Type 3A zeolite. The adsorption of the water generates heat, known as the heat of adsorption. The water adsorption process removes water from the process stream 20, and produces a dehydrated effluent stream 24. Dehydrated product stream 24 can have a significantly reduced weight percentage of water as compared to process stream 20. For example, dehydrated product stream 24 can be less than 5% water by weight, less than 2% water by weight, or less than 1% water by weight. In one example, dehydrated product stream 24 contains from about 0.25% water by weight to about 1.25% water by weight. Dehydrated product stream 24 exits the first temperature controlled adsorber 12, and can be utilized in its desired application.
The heat of adsorption of the water that is generated in first temperature controlled adsorber 12 is removed by indirect heat exchange with a cooling fluid 22. Cooling fluid 22 is provided to the one or more heat transfer flow passages 18 of the first temperature controlled adsorber 12, and exits the first temperature controlled adsorber 12 as heated cooling fluid 26.
When first temperature controlled adsorber 12 is undergoing adsorption, second temperature controlled adsorber 14 undergoes regeneration. During regeneration, second temperature controlled adsorber 14 is isolated from process stream 20. A heating fluid 30 is provided to, and passes through, the one or more heat transfer flow passages 32 of the second temperature controlled adsorber 14. The heating fluid 30 provides heat via indirect heat exchange to the one or more adsorption flow passages 34 of the second temperature controlled adsorber 14. The heat provided by heating fluid 30 is preferably sufficient to provide the regeneration heat requirement for the one or more adsorption flow passages 34. Additionally, the pressure in the one or more adsorption flow passages 34 may be reduced to facilitate regeneration. As heating fluid 30 passes through the one or more heat transfer flow passages 32, it loses heat and exits the second temperature controlled adsorber 14 as cooled heating fluid 36. Water that was adsorbed by the adsorptive material coating in the one or more adsorption flow passages 34 during the previous adsorption cycle of the second temperature controlled adsorber 14 is removed from the adsorptive material coating and exits the second temperature controlled adsorber 14 as a water effluent stream 38.
In MFGE production process 100, beer stream 106, which is the effluent from fermentation of starches and lignocellulose, is provided to a solids separation unit 108, such as beer column. Beer stream 106 is be a water-rich mixture containing water, alcohols (primarily ethanol), soluble solids, and insoluble solids. Beer stream 106 can contain from about 70% by weight water to about 90% percent by weight water. Additionally, beer stream 106 can contain from about 3% by weight ethanol to about 20% by weight ethanol. Solids separation 108 produces a process stream 110 and bottoms stream 132. When solids separation unit 108 is a beer column, 99% by weight or greater of the ethanol in the fermentation beer stream 106 can typically be recovered in process stream 110 as a dilute ethanol and water mixture. Process stream 110 can contain from about 10% by weight water to about 85% by weight water. Process stream 110, or at least a portion of process stream 110, can be in a vapor phase. Bottoms stream 132 contains primarily water and solids.
Process stream 110 can be directed to either the first temperature controlled adsorber 102 or the second temperature controlled adsorber 104, depending upon which adsorber is undergoing an adsorption cycle. For illustrative purposes, temperature controlled adsorber 102 will be described as undergoing an adsorption cycle, while temperature controlled adsorber 104 will be described as undergoing a regeneration cycle. It should be understood that during operation, the temperature controlled adsorbers 102 and 104 are preferably each cycled through alternating adsorption and regeneration cycles. It should also be understood that each temperature controlled adsorber has sufficient connections and feeds to undergo either adsorption or regeneration, although only a portion of such connections and feeds are illustrated in
When first temperature controlled adsorber 102 is undergoing adsorption, process stream 110 is provided to one or more inlets of first temperature controlled adsorber 102. Process stream 110 flows through the one or more adsorption flow passages 112 of the first temperature controlled adsorber 102. Water is adsorbed by an adsorptive material coating in the one or more adsorption flow passages 112. In one example, the adsorptive material coating contains a polymer and a zeolite, such as, for example, a Type 4A or a Type 3A zeolite. The adsorption of the water generates heat, known as the heat of adsorption. The water adsorption process removes water from the process stream 110, and produces a MFGE product stream 114. MFGE product stream 114 can be less than 5% water by weight, less than 2% water by weight, or less than 1% water by weight. Preferably, MFGE product stream 114 contains from about 0.25% water by weight to about 1.25% water by weight, and most preferably contains up to about 0.5% water by weight, or less than about 0.5% water by weight. MFGE product stream 114 preferably contains greater than 98% by weight ethanol. MFGE product stream 114 exits the first temperature controlled adsorber 102, and can be utilized in its desired application.
The heat of adsorption of the water that is generated in first temperature controlled adsorber 102 is removed by indirect heat exchange with a cooling fluid 116. Cooling fluid 116 is provided to the one or more heat transfer flow passages 118 of the first temperature controlled adsorber 102, and exits the first temperature controlled adsorber 102 as heated cooling fluid 120.
When first temperature controlled adsorber 102 is undergoing adsorption, second temperature controlled adsorber 104 undergoes regeneration. During regeneration, second temperature controlled adsorber 104 is isolated from process stream 110. A heating fluid 122 is provided to and passes through the one or more heat transfer flow passages 124 of the second temperature controlled adsorber 104. The heating fluid 122 provides heat via indirect heat exchange to the one or more adsorption flow passages 126 of the second temperature controlled adsorber 104. The heat provided by heating fluid 122 is preferably sufficient to provide the regeneration heat requirement for the one or more adsorption flow passages 126. Additionally, the pressure in the one or more adsorption flow passages 126 may be reduced to facilitate regeneration. As heating fluid 122 passes through the one or more heat transfer flow passages 124, it loses heat and exits the second temperature controlled adsorber 104 as cooled heating fluid 128. Water that was adsorbed by the adsorptive material coating in the one or more adsorption flow passages 126 during the previous adsorption cycle of the second temperature controlled adsorber 104 is removed from the adsorptive material coating, and exits the second temperature controlled adsorber 104 as water effluent stream 130.
Preferably, temperature controlled adsorption systems and processes can operate at conditions approaching isothermal conditions. In such examples, one or more benefits over operating an adiabatic adsorbent system or process can be achieved. For example, the upper limit on water concentration in the fluid to be treated can also be eliminated, providing the ability for dehydration of extremely water-rich streams. Additionally, increased differential loading potential can be provided, with substantially lower loadings achieved during regeneration and higher loadings achievable during adsorption steps. Lower product dew-points, lower product dew-point specifications for water in the product stream, and smaller equipment size for a given duty can be also achieved. Other benefits can include reduction of purge gas requirements during the regeneration step and simultaneous increase of the potential for recovering high concentrations of adsorbate (i.e. water) in the regeneration gas. Flexibility in selecting the heating and cooling heat transfer media with minimal impact on desired process streams can also be provided. Further, extremely rapid thermal swing adsorption with cycle times at or below current adiabatic PSA separation processes can be achieved, which can result in smaller adsorber systems, which saves both capital and energy.
From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.
