referring to the attached drawing there is shown a steam drum separator unit 10 which is surrounded by a plurality of individual heat exchanger units 11 . for example , six to eight heat exchanger units may be used with a single steam drum separator unit although the number will depend upon the thermal process steam that is to be generated as well as the steam conditions desired . the steam drum contains water , for example , up to the level 12 which is used to supply the water to the individual heat exchangers with the water being supplied through a conduit 13 to the bottom 14 of the individual exchangers . normally , thermal convection can be used to provide the necessary circulation between the steam drum to the exchangers and back to the steam drum although , in some cases , it may be necessary to use a pump 15 to supply the necessary circulation , particularly in cases where high flow rates and heat transfer rates are required . the steam exits from the top of the vertical exchangers and passes out the line 20 into the top of the steam drum . from the top of the steam drum the steam must pass around suitable separating units such as the baffle 21 before it can exit from the steam drum through the line 22 . the separating units serve to remove the excessive moisture contained in the steam which then falls back into the bottom of the steam drum where it can be recirculated to the individual exchangers . the individual heat exchangers are supplied with steam which is bled from the turbines of a cogeneration plant or similar sources through a line 30 . the steam exits from the exchangers through the line 31 back to the cogeneration plant where it can be used for additional heat exchangers or condensed to supply feed water for the boilers . the blow down line 40 and pump unit 41 are provided for periodically blowing down the steam drum to reduce the solids concentration in the water contained therein . the blow down discharge from the pump is supplied back to the outlet steam line 22 where the water can combine with the steam and be carried with the steam into the formation . in place of recirculating the solids to the steam line , the blow down can be discharged into a suitable disposal area if desired . since the heat exchange takes place in a single pass through the individual heat exchange units 11 the solids contained in the brackish feed water will not be deposited as scale on the heat exchanger tubes . the heat exchangers are designed to produce 80 - 85 percent quality steam with the solids contained in the wet steam that exits from the top of the individual units . of course , both the flow rate of the bleed steam and water through the heat exchangers must be maintained at controlled levels to ensure that the steam quality is maintained . even though separators are used to provide relatively dry steam the solids will concentrate in the steam drum 10 and not in the heat exchangers . while the solids are concentrated in the water in the steam drum , the solids will not be condensed and form scale on the steam drum since there is sufficient water in the steam drum to maintain them in solution . further , by periodically blowing down the steam drum the concentration of solids can be maintained within reasonable limits . the use of individual heat exchangers provides not only simplified construction but also additional reliability . the individual exchangers can be removed from service for repair of tube leaks and similar malfunctions while substantially full capacity of the system is maintained . since the steam drum separating unit 10 contains no tubes and is of simplified construction , it is relatively maintenance free .