Method and apparatus for producing ammonia (NH3)

A method for producing ammonia (NH3) and introducing the produced ammonia (NH3) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitrogen oxides contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the method comprising:

• feeding dry urea from a supply container in a controlled amount to a reactor;
• disposing the dry urea in the reactor in contact with a heated metal surface to thereby effect flash pyrolysis resulting in the spontaneous separation of the dry urea into a gas mixture comprising the reaction products of ammonia (NH3) and isocyanic acid (HCNO);
• and
• substantially immediately after the flash pyrolysis, catalytically treating the thus produced gas mixture in the presence of water via a quantitative hydrolysis treatment such that the isocyanic acid (HCNO) resulting from the flash pyrolysis is converted into ammonia (NH3) and carbon dioxide (CO2), whereby the water required for the quantitative hydrolysis treatment is comprised solely of a water-containing gas, and completely liquid water condensed from such water-containing gas, flowing in an exhaust gas partial stream that is branched, via an exhaust gas branch conduit, from the main exhaust gas stream resulting from the combustion process, the exhaust gas partial stream and the dry urea being fed in a quantitatively controlled amount into the reactor such that the quantity of water in the exhaust gas partial stream is appropriate for substantially complete conversion of the isocyanic acid (HCNO) resulting from the flash pyrolysis into ammonia (NH3) and carbon dioxide (CO2) with the quantity of the exhaust gas stream which is fed into the reactor being adjustably set as a function of the exhaust gas temperature such that the temperature for conversion is not exceeded;
• and
• conducting the ammonia (NH3) and carbon dioxide (CO2) generated by the catalytic hydrolysis treatment of the isocyanic acid (HCNO) into the exhaust gas stream at a location upstream of an SCR catalyzer, whereby ammonia (NH3) in the SCR catalyzer system is reinforced as the reduction means for the reduction of NOx.

A method for producing ammonia (NH3) and introducing the produced ammonia (NH3) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitrogen oxides contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the method comprising:

• feeding dry urea from a supply container in a controlled amount to a reactor;
• disposing the dry urea in the reactor in contact with a heated metal surface to thereby effect flash pyrolysis resulting in the spontaneous separation of the dry urea into a gas mixture comprising the reaction products of ammonia (NH3) and isocyanic acid (HCNO);
• and
• substantially immediately after the flash pyrolysis, catalytically treating the thus produced gas mixture in the presence of water via a quantitative hydrolysis treatment such that the isocyanic acid (HCNO) resulting from the flash pyrolysis is converted into ammonia (NH3) and carbon dioxide (CO2), whereby the water required for the quantitative hydrolysis treatment is comprised in an exhaust gas partial stream that is branched, via an exhaust gas branch conduit, from the main exhaust gas stream resulting from the combustion process, the exhaust gas partial stream and the dry urea being fed in a quantitatively controlled amount into the reactor such that the quantity of water in the exhaust gas partial stream is appropriate for substantially complete conversion of the isocyanic acid (HCNO) resulting from the flash pyrolysis into ammonia (NH3) and carbon dioxide (CO2), wherein the quantity of water (H2O) comprised in the exhaust gas partial stream that is required for the quantitative hydrolysis treatment of the isocyanic acid (HCNO) is controlled as a function of the exhaust gas treatment such that, in the event that the exhaust gas temperature is greater than the decomposition temperature of the dry urea, the exhaust gas partial stream flowed to the reactor for contact with the heated metal surface therein has a relatively larger mass flow than the exhaust gas partial stream has in the event that the exhaust gas temperature in less than the decomposition temperature of the dry urea, whereby the exhaust gas partial stream having the relatively larger mass flow correspondingly reduces the electricity needed to heat the heated metal surface;
• and
• conducting the ammonia (NH3) and the carbon dioxide (CO2) generated by the catalytic hydrolysis treatment of the isocyanic acid (HCNO) into the exhaust gas stream at a location upstream of an SCR catalyzer, whereby ammonia (NH3) in the SCR catalyzer system is reinforced as the reduction means for the reduction of NOx.

An apparatus for producing ammonia (NH3) and introducing the produced ammonia (NH3) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitric oxide contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the apparatus comprising:

• a storage container in which urea in dry form in the form of powder, granulate, or micro-prills is stored;
• a reactor for the production of ammonia (NH3) and having a heated reaction chamber which is partitioned into a thermal treatment zone and a hydrolysis treatment zone, and the reaction chamber of the reactor being disposed for the treatment therein of an exhaust gas stream from the combustion exhaust gases of a selected one of an internal combustion engine, a gas turbine and a burner;
• a device for feed of the urea, preferably in controlled or measured amounts, from the supply container into the reaction chamber of the reactor;
• an electrical heating element in the thermal treatment zone of the reaction chamber of the reactor;
• a device for controlling the temperature of the heating element in a manner such that the urea introduced into the reaction chamber is spontaneously de-composeable, via flash hydrolysis, into ammonia (NH3) and isocyanic acid (HCNO);
• a device for introducing water derived solely from a water-containing gas flowing the exhaust gas stream into the reaction chamber of the reactor, the device for introducing water includes a feed conduit and an electrically controllable blocking valve in the feed conduit and moveable between open and closed positions and, preferably, moveable as well into flow through amount-controlling intermediate positions, the movement of the blocking valve into its respective positions being controllable by the device for controlling the temperature of the heating element;
• and
• a hydrolysis catalyzer in the hydrolysis treatment zone of the reaction chamber of the reactor for converting, in the presence of water, the isocyanic acid (HCNO), which is produced from the flash hydrolysis of the urea in addition to ammonia (NH3), into ammonia (NH3) and carbon dioxide (CO2).