A flowhood assembly for treatment of an exhaust gas with a treatment fluid, the assembly including: a flowhood, an injector, and a mount for mounting the injector on the flowhood; the flowhood including: an exhaust flowpath, and a connection portion opening into the exhaust flowpath, the connection portion defining a connection axis; the injector including: a nozzle, the nozzle having an outlet end and defining an injection axis of the injector, a treatment fluid port connectable to a supply of treatment fluid to conduct the treatment fluid to the nozzle, and one or more coolant ports (34, 35) connectable to a supply of liquid coolant for cooling the injector in use; the injector being arranged in use to inject the treatment fluid from the outlet end of the nozzle along the injection axis into the exhaust flowpath; the flowhood having a normal use position defined by a predefined angle of the connection axis relative to a nominal horizontal plane; the mount having a design orientation defined as an upright rotational position of the mount about the connection axis relative to the nominal horizontal plane; the mount being fixable to the connection portion of the flowhood in any of a plurality of alternative connected positions of the mount defined by rotation of the flowhood about the connection axis relative to the mount in the normal use position of the flowhood and the design orientation of the mount; characterized in that the injector being fixable to the mount in any of a plurality of alternative mounted positions of the injector, said alternative mounted positions being defined by rotation of the injector with respect to the mount about the injection axis through a range of second rotational positions angularly intermediate said alternative mounted positions; wherein the injector is not fixable to the mount in said second rotational positions; and in each of said alternative mounted positions of the injector, when the mount is fixed to the connection portion in the design orientation of the mount and the normal use position of the flowhood and in any of said alternative connected positions of the mount: the injection axis is inclined downwardly away from the injector relative to the nominal horizontal plane; and at least one said coolant port (34, 35) is arranged above a horizontal plane passing through the injection axis at the outlet end of the nozzle. a flowhood, an injector, and a mount for mounting the injector on the flowhood; the flowhood including: an exhaust flowpath, and a connection portion opening into the exhaust flowpath, the connection portion defining a connection axis; an exhaust flowpath, and a connection portion opening into the exhaust flowpath, the connection portion defining a connection axis; the injector including: a nozzle, the nozzle having an outlet end and defining an injection axis of the injector, a treatment fluid port connectable to a supply of treatment fluid to conduct the treatment fluid to the nozzle, and one or more coolant ports (34, 35) connectable to a supply of liquid coolant for cooling the injector in use; a nozzle, the nozzle having an outlet end and defining an injection axis of the injector, a treatment fluid port connectable to a supply of treatment fluid to conduct the treatment fluid to the nozzle, and one or more coolant ports (34, 35) connectable to a supply of liquid coolant for cooling the injector in use; the injector being arranged in use to inject the treatment fluid from the outlet end of the nozzle along the injection axis into the exhaust flowpath; the flowhood having a normal use position defined by a predefined angle of the connection axis relative to a nominal horizontal plane; the mount having a design orientation defined as an upright rotational position of the mount about the connection axis relative to the nominal horizontal plane; the mount being fixable to the connection portion of the flowhood in any of a plurality of alternative connected positions of the mount defined by rotation of the flowhood about the connection axis relative to the mount in the normal use position of the flowhood and the design orientation of the mount; characterized in that the injector being fixable to the mount in any of a plurality of alternative mounted positions of the injector, said alternative mounted positions being defined by rotation of the injector with respect to the mount about the injection axis through a range of second rotational positions angularly intermediate said alternative mounted positions; wherein the injector is not fixable to the mount in said second rotational positions; and in each of said alternative mounted positions of the injector, when the mount is fixed to the connection portion in the design orientation of the mount and the normal use position of the flowhood and in any of said alternative connected positions of the mount: the injection axis is inclined downwardly away from the injector relative to the nominal horizontal plane; and at least one said coolant port (34, 35) is arranged above a horizontal plane passing through the injection axis at the outlet end of the nozzle. the injection axis is inclined downwardly away from the injector relative to the nominal horizontal plane; and at least one said coolant port (34, 35) is arranged above a horizontal plane passing through the injection axis at the outlet end of the nozzle.