Exhaust after-treatment system including ammonia and hydrogen generation

An after-treatment system including an exhaust treatment component provided in an exhaust passage, a tank carrying an aqueous reagent, and an electrochemical cell in communication with the tank and configured to receive the aqueous reagent therefrom. The electrochemical cell is configured to convert the aqueous reagent into a first exhaust treatment fluid and a second exhaust treatment fluid. A controller is in communication with the electrochemical cell. The controller is configured to vary amounts and/or composition of each of the first exhaust treatment fluid and the second exhaust treatment fluid produced by the electrochemical cell. An injector is in communication with the electrochemical cell and the exhaust passage, and is configured to receive one of the first exhaust treatment fluid or the second exhaust treatment fluid from the electrochemical cell, and dose the one exhaust treatment fluid into the exhaust passage at a location upstream from the exhaust treatment component.

FIELD

The present disclosure relates to an exhaust after-treatment system that includes an electrochemical cell that produces ammonia and hydrogen in a plurality of blends for after-treatment of exhaust gases.

BACKGROUND

In an attempt to reduce the quantity of NOxand particulate matter emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment devices have been developed. A need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented. Typical aftertreatment systems for diesel engine exhaust may include one or more of a diesel particulate filter (DPF), a selective catalytic reduction (SCR) system (including a urea injector), a hydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC).

Although urea that converts to ammonia in the exhaust stream is useful for assisting in the reduction of NOx using SCR, the use of ammonia that is formed before being provided to the exhaust stream provides greater efficacy in reducing NOx. Further, the use of hydrogen can be useful for regenerating a DPF or other catalyst-coated substrates. It is desirable, therefore, to develop various systems and methods for generating ammonia and hydrogen for exhaust after-treatment.

SUMMARY

The present disclosure provides an after-treatment system including an exhaust treatment component provided in an exhaust passage, a tank carrying an aqueous reagent, and an electrochemical cell in communication with the tank and configured to receive the aqueous reagent therefrom. The electrochemical cell is configured to convert the aqueous reagent into a first exhaust treatment fluid and a second exhaust treatment fluid. A controller is in communication with the electrochemical cell. The controller is configured to vary amounts and/or composition of each of the first exhaust treatment fluid and the second exhaust treatment fluid produced by the electrochemical cell. An injector is in communication with the electrochemical cell and the exhaust passage, and is configured to receive one of the first exhaust treatment fluid or the second exhaust treatment fluid from the electrochemical cell, and dose the one exhaust treatment fluid into the exhaust passage at a location upstream from the exhaust treatment component.

DETAILED DESCRIPTION

FIG. 1schematically illustrates an exemplary exhaust system10according to a principle of the present disclosure. Exhaust system10can include at least an engine12in communication with a fuel source (not shown) that, once consumed, will produce exhaust gases that are discharged into an exhaust passage14having an exhaust after-treatment system16. Engine12may be an engine for a vehicle such as a car, truck, locomotive, or marine vessel, or an engine used in a stationary power plant application. Downstream from engine12can be disposed a pair of exhaust treatment components18and20, which can include catalyst-coated substrates or filters22and24. Catalyst-coated substrates or filters22and24can be any combination of a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC) component, a selective catalytic reduction (SCR) component, a lean NOxcatalyst (LNC), an ammonia slip catalyst, or any other type of exhaust treatment device known to one skilled in the art. If a DPF is used, it may be catalyst-coated (e.g., DOC catalyst coated, SCR catalyst-coated, or some other type of catalyst-coated substrate). In the illustrated embodiment, substrate22includes a DPF component, and substrate24includes an SCR component.

Although not required by the present disclosure, exhaust after-treatment system16can further include components such as a thermal enhancement device or burner26to increase a temperature of the exhaust gases passing through exhaust passage14. Increasing the temperature of the exhaust gas is favorable to achieve light-off of the catalyst in the exhaust treatment component18in cold-weather conditions and upon start-up of engine12, as well as initiate regeneration of the exhaust treatment component18when the exhaust treatment substrate22is a DPF.

To assist in reduction of the emissions produced by engine12, exhaust after-treatment system16can include dosing modules or injectors28and38for periodically dosing a first exhaust treatment fluid and a second exhaust treatment fluid, respectively, into the exhaust stream. As illustrated inFIG. 1, injector28can be located upstream of exhaust treatment component18, and is operable to inject the first exhaust treatment fluid into the exhaust stream that is selected to, for example, improve light-off of the catalysts of the catalyst-coated substrates22and24. Injector38can be located upstream of exhaust treatment component20, and is operable to inject the second exhaust treatment fluid to the exhaust stream that is operable to, for example, assist in the reduction of NOx in the exhaust stream.

More specifically, according to the present disclosure, injectors28and38are in fluid communication with an electrochemical cell29, with the electrochemical cell receiving an aqueous urea solution from a reagent tank30and a pump32by way of inlet line34. Although not required by the present disclosure, electrochemical cell29may be in communication with reagent tank30via return line36. Return line36allows for any urea solution that does not undergo electrochemical reaction to be returned to reagent tank30.

As will be described in more detail below, the aqueous urea solution undergoes electrochemical treatment in electrochemical cell29to produce gaseous fluids comprising ammonia (NH3) and hydrogen (H2). The fluid comprising hydrogen may then then fed to injector28, which doses the fluid comprising hydrogen into the exhaust passage14upstream from DPF22to raise the exhaust temperature and assist with regenerating DPF (i.e., assist in removing the build-up of soot). The produced fluid comprising ammonia may be fed to injector38, which doses the fluid comprising ammonia into the exhaust passage14upstream of SCR substrate24to enhance removal of NOx from the exhaust stream. Although exhaust system16is designed to provide fluids comprising hydrogen and ammonia to injectors28and38, respectively, after passing through electrochemical cell29, it should be understood that cell29may be bypassed such that the aqueous urea solution in reagent tank30may be directly provided to an injector39configured for liquid dosing via injector inlet line41.

The activation of downstream catalysts is enhanced by using the hydrogen-comprising fluid to raise exhaust temperatures. In this regard, the use of the fluid comprising hydrogen improves light-off and conversion efficiencies for nearly all types of catalysts, which enables greater conversion efficiencies at lower temperatures, enhances cold start and low-load duty cycle response, which are areas of focus for reductions in exhaust emissions.

In addition, the use of the fluid comprising hydrogen produced by cell29can be used to aid in NOx conversion in an LNC system, and assist in reducing byproduct emissions that typically would require additional catalyst cleanup. Other systems that benefit from the use of hydrogen produced by cell29include NOx adsorbers. In this regard, the hydrogen may be used to regenerate the adsorber in a manner similar to a DPF (i.e., reduce soot). Yet another benefit of the hydrogen produced by cell29is that the fluid comprising hydrogen may be reacted with carbon dioxide for the generation of on-board hydrocarbons, which may then be used in dual fuel applications (i.e., engine applications that include more than a single fuel sources such as a ship or stationary application), Alternatively, the fluid comprising hydrogen may be fed to engine12to improve combustion, which reduces emissions while improving fuel efficiency. Additional benefits of a fluid comprising hydrogen being fed to engine12include resolving engine knock, reduces the amount of NOx generated during combustion, and reduction in in-cylinder particulate matter.

The amount of ammonia required to effectively treat the exhaust stream may vary with load, engine speed, exhaust gas temperature, exhaust gas flow, engine fuel injection timing, desired NOxreduction, barometric pressure, relative humidity, EGR rate and engine coolant temperature. A NOxsensor or meter40may be positioned downstream from exhaust treatment component24. NOxsensor40is operable to output a signal indicative of the exhaust NOxcontent to an engine control unit42. All or some of the engine operating parameters may be supplied from engine control unit40via the engine/vehicle databus to a reagent electronic dosing controller44. The reagent electronic dosing controller44could also be included as part of the engine control unit42. Exhaust gas temperature, exhaust gas flow and exhaust back pressure and other vehicle operating parameters may be measured by respective sensors, as indicated inFIG. 1.

The amount of exhaust treatment fluid required to effectively treat the exhaust stream can also be dependent on the size of the engine12. In this regard, large-scale diesel engines used in locomotives, marine applications, and stationary applications can have exhaust flow rates that exceed the capacity of the single injectors28and38. Accordingly, although only a single injector28is illustrated for dosing a fluid comprising hydrogen and only a single injector38is illustrated for dosing a fluid comprising ammonia (or for dosing aqueous urea), it should be understood that multiple injectors28and38for hydrogen and ammonia injection are contemplated by the present disclosure.

An exemplary electrochemical cell29is illustrated inFIG. 2. Electrochemical cell29may include a reaction chamber46, which may be made of materials such as steel that are not degraded by the alkaline electrolyte composition held by reaction chamber46. An anode48and a cathode50are suspended within an alkaline electrolyte composition52contained in chamber46. A separator53is positioned between the anode48and the cathode50so that the product streams comprising ammonia and hydrogen produced at each of the anode48and cathode50, respectively, may be separately routed to injectors28and38, respectively. The alkaline electrolyte composition52includes an effective amount of aqueous urea received from reagent tank30. Anode48and cathode50are electrically connected to a power source54, such as a voltage source, which provides the electrical energy for the electrolysis of the aqueous urea contained in the alkaline electrolyte composition52. Although not illustrated, chamber46may include a stirring device that intermixes the aqueous urea and alkaline electrolyte composition52.

The electrodes48and50can each include a conductor or a support which can be coated with one or more active conducting components. Exemplary conductors include, but are not limited to, metals such as nickel and platinum, alloys such as carbon steel or stainless steel, or other materials capable of conducting electricity such as carbon or graphite. Exemplary electrode support materials may be chosen from many known supports, such as foils, meshes, and sponges, for example. The support materials may include, but are not limited to, Ni foils, Ti foils, graphite, carbon fibers, carbon paper, glassy carbon, carbon nanofibers, and carbon nanotubes. Aside from these specific support materials listed, other suitable supports will be recognized by those of ordinary skill in the art.

The anode48may include a conductor that is inert to the alkaline electrolyte composition52. Additionally, the anode48may further include a support material that is inert to the alkaline electrolyte compositions52and coated with one or more active conducting components. According to embodiments of the present disclosure, the reaction of urea hydrolysis occurs at the conducting component of the anode48. Therefore, the conductor and/or the conducting component at the anode48include one or more metals active toward electrolytic hydrolysis of urea. Active metals may include cobalt, copper, iridium, iron, platinum, nickel, rhodium, ruthenium, or mixtures or alloys thereof, for example, and in particular, nickel. The active metals may be in an oxidized form, such as nickel oxyhydroxide.

The cathode50may include a conductor that is inert to the alkaline electrolyte composition52. Additionally, the cathode50may further include a support material that is inert to the alkaline electrolyte compositions and coated with one or more active conducting components. For example, the conducting component of the cathode may include carbon, cobalt, copper, iridium, iron, nickel, palladium, platinum, rhodium, ruthenium, or mixtures or alloys thereof. Exemplary conducting components include carbon steel and stainless steel.

The structure of the anode48and cathode50is not limited to any specific shape or form. For example, the active metal may be formed as foil, wire, gauze, bead, or coated onto a support. Alternatively, the anode48and cathode50may be formed as a series of electrode plates, cylindrical elements, wavy elements, or Swiss roll types of electrodes.

The separator53separates the anode48from the cathode50. Separator53is generally constructed from materials chemically resistant to the alkaline electrolyte composition52. Many polymers are suitable for constructing separator53, including materials such as TEFLON® and polypropylene. Alternatively, separator53may be an ion exchange membrane, a solid electrolyte, or an electrolytic gel, for example. Further, the separator53may be permeable, semi-permeable or impermeable to gases or liquids.

The electrolyte composition52is preferably alkaline. Accordingly, the alkaline electrolyte composition52may include a sufficient quantity of any suitable hydroxide salt, carbonate salt, or bicarbonate salt. An alkali metal hydroxide or alkaline earth metal hydroxide salt, such as lithium hydroxide, rubidium hydroxide, cesium hydroxide, barium hydroxide, strontium hydroxide, potassium hydroxide, sodium hydroxide, magnesium hydroxide, calcium hydroxide, and mixtures thereof may also be used. Similarly, alkali metal carbonates or bicarbonate salts or alkaline earth metal carbonates or bicarbonate salts are also suitable electrolytes. The alkaline electrolyte composition52may also include a gel, such as a solid polymer electrolyte. Suitable gels include, but are not limited to, those containing polyacrylic acid, polyacrylates, polymethacrylates, polyacrylamides and similar polymers and copolymers.

Voltage source54may be any available source, such as a vehicle battery (not shown), vehicle alternator, or fuel cell. In the case of a stationary application, the voltage source may be power from a grid, or from a renewable energy source such as a solar cell or a wind-turbine generator, for example. Other voltage sources known to those skilled in the art may also be used. Regardless of the source of voltage, a voltage sufficient to initiate the electrolytic hydrolysis of urea is required. Generally, the minimum voltage required to electrolyze or electrolytically hydrolyze urea is about 0.85 volts.

Additionally, according to the present disclosure the rate of producing fluids comprising ammonia and hydrogen from the aqueous urea solution may be controlled by varying the voltage to electrochemical cell29. In this regard, voltage source54is configured to apply a voltage potential to electrochemical cell29such that a voltage difference exists between anode48and cathode50. In addition, a variable ground or reference voltage potential may be applied to electrochemical cell29. By varying the voltage difference between the anode48and the cathode50, the amounts of ammonia and hydrogen in each fluid produced at anode48and cathode50can also be varied. In this manner, the amounts of ammonia-containing fluid and hydrogen-containing fluid can be tailored as desired.

The voltage potentials provided by voltage source54to electrochemical cell29can be controlled by ECU42or controller44. For example, controller44is configured to determine the amount of NOx being produced by engine12based on a signal received from NOx sensor40. Controller44, therefore, can instruct voltage source54to adjust the voltage difference between anode50and cathode to either increase or decrease ammonia production by electrochemical cell29. Alternatively, controller44is configured to determine the correct voltage difference between anode48and cathode50based on crank position, engine load, RPM, exhaust volume, exhaust temperature, and the like. In this manner, the amounts of ammonia and hydrogen produced can be independently increased or decreased dynamically.

After the hydrogen and ammonia gases are generated at anode48and cathode50, respectively, the mixture of gases exit electrochemical cell29through outlet55where the mixture of gases are then routed to either injector28or injector38and dosed into the exhaust stream. In this regard, outlet55includes a valve57that can direct the mixture of gases toward injector28or to injector38. Alternatively, valve57can be used to split a portion of the gas mixture towards injector28, and split a portion of the gas mixture towards injector38. Regardless, as noted above, electrochemical cell29can be operated in a manner where various blends of hydrogen and ammonia can be produced. Based on the desired operating conditions of exhaust system16, the use of valve57allows for various blends of the gas mixture to be directed to the desired injector(s)28and/or38as needed or desired.

Now referring toFIG. 3, it can be seen that exhaust after-treatment system16may include a plurality of electrochemical cells29, with each of the voltage sources54associated with each cell29being in communication with controller44. Alternatively, each voltage source54can additionally be in communication with ECU42or only in communication with ECU42. It should be understood that although three electrochemical cells29a,29b, and29care illustrated, a greater or lesser number of cells29can be utilized without departing from the scope of the present disclosure.

Each voltage source54is independently in communication with controller44or ECU42and, therefore, each electrochemical cell29can be separately controlled. Thus, the amounts of ammonia and hydrogen produced by each cell29can be independently adjusted to produce a plurality of different blends of ammonia and hydrogen for exhaust after-treatment and engine combustion. For example, all the cells29a-29ccan be directed by controller44or ECU42to produce only or more ammonia in comparison to hydrogen, or all the cells29a-29ccan be directed by controller44or ECU42to produce only or more hydrogen in comparison to ammonia. Alternatively, some of the cells29(e.g.,29aand29b) can be used to produce or increase ammonia production, and one of the cells29(e.g.,29c) can be used to produce or increase hydrogen production. Still alternatively, a single cell (e.g.,29a) can be used for ammonia production and the remaining cells (e.g.,29band29c) can be used for hydrogen production or vice versa. In other embodiments, a number (e.g., 1, 2, or 3) of the cells (e.g.,29a) can be used to produce hydrogen for engine combustion, while another number (e.g., 1 or 2) of the cells can be used for exhaust after-treatment. Further, any number of the cells29ato29ccan be deactivated as needed. Any number of different combinations of using the cells29ato29cis contemplated for ammonia and hydrogen production.

Each cell29a,29b, and29cincludes an outlet55that may be opened and closed by a valve57, with valves57each being in communication with controller44or ECU42. With this configuration, valves57can be controlled to direct the mixture of gases produced by cells29a,29b, and29cto either injector28or to injector38. Alternatively, valves57can be used to split a portion of the gas mixture towards injector28, and split a portion of the gas mixture towards injector38. Regardless, as noted above, electrochemical cells29a,29b, and29ccan each be operated in a manner where various blends of hydrogen and ammonia can be produced. Based on the desired operating conditions of exhaust system16, the use of valves57allow for various blends of the gas mixture to be directed to the desired injector(s)28and/or38as needed or desired.

FIG. 3also illustrates the use of temperature control devices59that are associated with each electrochemical cell29a,29b, and29c. Temperature control devices59may be used to either heat or cool electrochemical cells29a,29b, and29cto further tailor the amounts of hydrogen and ammonia produced by each cell. That is, the use of temperature can also influence the reaction characteristics at anode48and cathode50to an extent that affects the production of hydrogen and ammonia. Because each temperature control device59is in communication with controller44or ECU42, each cell29a,29b, and29ccan be independently adjusted to influence the blend of gases produced by each cell.

Now referring toFIG. 4, it can be seen that an electrochemical cell29is in communication with a hydrogen gas accumulator61and an ammonia gas accumulator63. Although only a single electrochemical cell29is illustrated inFIG. 4, it should be understood that a plurality of electrochemical cells (e.g., the electrochemical cells29a,29b, and29cillustrated inFIG. 3) can be used without departing from the scope of the present disclosure. According to the configuration illustrated inFIG. 4, aqueous urea reagent is fed from tank30by pump32to electrochemical cell(s)29after passing through bypass valve65. Alternatively, bypass valve65, which is controlled by controller44or ECU42, may direct the aqueous urea reagent directly to injector38through bypass line39. Although onlyFIG. 4illustrates the use of bypass valve65, it should be understood that any of the configurations illustrated inFIGS. 1-7can include a bypass valve67and bypass line39to provide the aqueous urea reagent directly to injector38.

After receipt of the aqueous urea reagent by electrochemical cell(s)29, the production of ammonia or hydrogen is conducted as described above. More specifically, electrochemical cell(s)29are directed to produce either ammonia or hydrogen by controlling voltage source54with controller44or ECU42. The ammonia or hydrogen produced by electrochemical cell(s)29then exits electrochemical cell(s) through outlet55where valve67is placed to direct the gases to the desired accumulator61or63. That is, if hydrogen gas is produced by electrochemical cell(s)29, the valve67directs the hydrogen gas to the hydrogen gas accumulator61. If ammonia gas is produced by electrochemical cell(s)29, the valve67directs the ammonia gas to ammonia gas accumulator63. The accumulators61and63may then store the hydrogen and ammonia gases, respectively, until needed by exhaust system16. When the gases are needed by the exhaust system16, accumulators61and63may then feed injectors28and38for dosing into the exhaust stream. To control feeding of the gases to injectors28and38, accumulators61and63may include mechanical or electro-mechanical outlets (not shown) that are controlled by controller44or ECU42.

Now referring toFIG. 5, it can be seen that exhaust after-treatment system16may include a plurality of electrochemical cells29, with each of the voltage sources54associated with each cell29being in communication with controller44. Alternatively, each voltage source54can additionally be in communication with ECU42or only in communication with ECU42. It should be understood that although four electrochemical cells29a,29b,29c, and29dare illustrated, a greater or lesser number of cells29can be utilized without departing from the scope of the present disclosure.

Each voltage source54is independently in communication with controller44or ECU42and, therefore, each electrochemical cell29can be separately controlled. Thus, the amounts of ammonia and hydrogen produced by each cell can be independently adjusted to produce a plurality of different blends of ammonia and hydrogen for exhaust after-treatment and engine combustion. For example, all the cells29a-29dcan be directed by controller44or ECU42to produce only or more ammonia in comparison to hydrogen, or all the cells29a-29dcan be directed by controller44or ECU42to produce only or more hydrogen in comparison to ammonia. Alternatively, half of the cells29(e.g.,29aand29b) can be used for or to produce or increase ammonia production, and half of the cells29(e.g.,29cand29d) can be used to produce or increase hydrogen production. Still alternatively, a single cell (e.g.,29a) can be used for ammonia production and the remaining cells (e.g.,29b-29d) can be used for hydrogen production or vice versa. In other embodiments, a number (e.g., 1, 2, or 3) of the cells (e.g.,29a) can be used to produce hydrogen for engine combustion, while another number (e.g., 1, 2, or 3) of the cells can be used for exhaust after-treatment. Further, any number of the cells29ato29dcan be deactivated as needed. Any number of different combinations of using the cells29ato29dis contemplated for ammonia and hydrogen production.

Although the cells29ato29dinFIG. 5are illustrated as being separate and apart from each other and in communication with their own corresponding injectors28and38via outlets56and58, respectively, the present disclosure should not be limited thereto. For example, as illustrated inFIG. 6, the outlet lines56and58for ammonia and hydrogen, respectively, may feed into feed lines60and62that are common to each cell29. Feed lines60and62may then be in communication with a single injector28or38, or in communication with a plurality of injectors28or38through the use of additional lines64and valves66(FIG. 7), with the valves66being in communication with controller44or ECU42so that the desired location of the ammonia or hydrogen can be controlled by opening and closing the various valves66. Alternatively, the cells29ato29dcan be in a stacked arrangement as illustrated inFIG. 6.

As noted above, the adjustment of voltage to each of the anode48and cathode50can be used to tailor the amounts and/or composition of ammonia and hydrogen produced by each cell29. Similarly, the adjustment of current applied to the anode48and cathode50can also be used to affect performance of the cell29. Assuming that the voltage applied to each of the anode48and cathode50is constant, the current applied to anode48and cathode50can be varied by adjusting the resistance of the cell29. More particularly, the current can be adjusted by either raising or lowering the resistance of the cell29. To adjust the resistance of the cell29, the concentration of the aqueous urea reagent can be changed by either increasing or decreasing the amount of aqueous urea reagent provided to cell29. This can be done by either increasing or decreasing the flow rate of the aqueous urea reagent into the cell29by adjusting operation of pump32. Alternatively, increasing or decreasing the concentration of the electrolyte52can affect the resistance of the cell29. In this regard, although not illustrated in the drawings, it should be understood that the alkaline electrolyte52can be continually recycled using a tank (not shown) and inlets and outlets that allow the electrolyte52to be recharged. Similar to the aqueous urea reagent, the flow rate of the alkaline electrolyte52to cell can be adjusted to affect the concentration thereof.

In addition, if the anode48is formed of nickel, it is believed that the formation of nickel oxyhydroxide (NiOOH) at the surface of anode48assists in catalyzing the formation of ammonia from the aqueous urea reagent. The formation of nickel oxyhydroxide can either be increased or decreased by adjusting the current applied to the anode48. Accordingly, to increase the amount of ammonia produced by cell29, the current applied to anode48can be increased by increase the formation the nickel oxyhydroxide and, therefore, increase the rate of production of ammonia. Alternatively, if a lower production of ammonia is desired, the formation of nickel oxyhydroxide can be reduced by lowering the current applied to anode48. Regardless, it should be understood that various blends of ammonia and hydrogen can be produced by each cell29by adjusting the current applied to the anode48and cathode50. Although the resistance of the cell29can be affected by adjusting either the aqueous urea concentration or the electrolyte52concentration, it should be understood that the resistance can be altered in other ways as well. For example, the addition of a salt, acid or base can also be used to modify the resistance of the cell.

The electrical current may also be used to control the production of ammonia from the electrolytic hydrolysis of urea and therefore control the rate of injecting ammonia into an exhaust gas treatment system. For example, a given electrical current may be required to induce the active form of the active metal in all the regions of the anode to maximize the production of ammonia. The applied current may be lowered when the need for ammonia decreases.

It should also be understood that the cell29may operate over varying ranges of pressure and temperature. Preferably, the pressure may be about atmospheric or ambient pressure. With respect to temperature, a preferably temperature range for operating the cell29may range between about 0 C to about 100 C. Temperatures above 100 C are generally not desirable from the standpoint of prevent unwanted co-reactions from taking place within the cell. Exemplary unwanted co-reactions include the aqueous urea solution undergoing thermolysis reactions that can produce unwanted byproducts such as biuret, cyanuric acid, ammelide, ammeline, and melamine. In addition, temperatures near or above 100 C can result in excessive evaporation rates of fluid within cell29. Regardless, it should be understood that the temperature of cell29may be controlled with any available source. For example, the electrolytic cell29may include a heater apparatus such as a heating jacket that surrounds the chamber46, from which heat may be supplied by providing exhaust gases to the jacket. Alternatively, an electric heater may be provided to the cell29.