Heat exchange structure

Claim 1

A BOILER COMPRISING A SHELL DEFINING AN ENCLOSURE, HEATING MEANS FOR PROVIDING HOT FLUID IN HEAT EXCHANGE PROXIMITY WITH SAID ENCLOSURE, A PAIR OF OPPOSING FACING TUBE SHEETS GENERALLY VERTICALLY MOUNTED WITHIN SAID SHELL ADJACENT OPPOSIING ENDS OF SAID ENCLOSURE AND DEFINING A CHAMBER THEREBETWEEN WITHIN SAID ENCLOSURE, AN INLET AND OUTLET THROUGH SAID SHELL FOR DELIVERING FEED TO AND DELIVERING PRODUCT FROM SAID CHAMBER, A PLURALITY OF GENERALLY HORIZONTALLY DISPOSED HEAT EXCHANGE TUBES MOUNTED THROUGH SAID CHAMBER IN HEAT EXCHANGE THEREWITH, EACH OF SAID TUBES HAVING OPPOSING OPEN ENDS COMMUNICATING WITH SAID ENCLOSURE EXTERIORLY OF SAID CHAMBER AND BEYOND SAID TUBE SHEETS, AND MEANS FOR DIRECTING HOT COMBUSTION GASES FROM SAID HEATING MEANS TO AN INLET END OF EACH HEAT EXCHANGE TUBE, EACH HEAT EXCHANGE TUBE COMPRISING A TUBULAR MEMBER HAVING AN INNER SURFACE INCLUDING A PLURALITY OF BOSSES IN SPIRAL ARRAY DEFINING A SPIRAL BRUSH CLEANING PATH THROUGH THE TUBE BETWEEN THE BOSSES, EACH CONVOLUTION OF SAID SPIRAL ARRAY COMPRISING A PLURALITY OF SPACED SEPARATE BOSSES, SAID BOSSES IN EACH CONVOLUTION OF SAID SPIRAL ARRAY BEING ALIGNED LINEARLY RELATIVE TO BOSSES IN THE REMAINING CONVOLUTIONS DEFINING A STRAIGHT BRUSH CLEANING PATH THROUGH THE TUBE BETWEEN THE BOSSES INCLUDING AN UNBOSSED SURFACE COMPRISING A TROUGH TRAVERSING CONVOLUTIONS OF THE SPIRAL ARRAY AND EXTENDING FROM ONE END OF THE TUBE TO THE OTHER, SAID TUBES BEING DISPOSED AND MOUNTED BY SAID TUBE SHEETS INCLINED LENGTHWISE SLIGHTLY FROM HORIZONTAL FROM ONE END TO THE OTHER WITH SAID UNBOSSED TROUGH SURFACE DISPOSED AT THE BOTTOM OF EACH TUBE FOR GRAVITY DRAINAGE OF CONDENSATE ACROSS THE SPIRAL PATH DEFINED BY SAID BOSES AND FROM THE TUBE.