used in fig3 designate like parts in fig4 is an evaporator and in fig5 is a mixing drum and 10 is a distribution drum fig6 shows other components a heater 11 a deaerator 14 a boiler feed pump 15 and an orifice 16 in fig7 and 8 the numeral 4 denotes a center wall tube bank the arrangements in fig4 and 8 require no pump or heater where the tubes are branched off from a preboiler unit to provide a nozzle assembly that is in the mode of arrangement of fig6 the invention will be embodied as shown in fig9 a the chemicals feeding nozzle assembly 1 is formed by tubes branched off from the outlet of a front high pressure feedwater heater 11a and returned to the inlet of an economizer 17 bypassing a rear high pressure feedwater heater 11b where the tubes come from the boiler unit or in the mode of fig4 the embodiment will be as illustrated in fig9 b here the chemicals feeding nozzle assembly 1 is located between furnaces 2a and 2b the numeral 18 indicates a superheater a similar case of tube branching from the boiler unit as indicated in fig7 will be embodied as in fig9 c the latter figure shows the chemicals feeding nozzle assembly 1 formed by tubes branched off from.