Vertical multiple passage drainable heated surfaces with headers-equalizers and forced circulation

Abstract

The present invention discloses improved heated surfaces (HS) with vertical multiple passage panels or vertical serpentine coils from straight tubes with connections between them by top and bottom bends. In HS with tube bends there is not any mixing headers—each circuit has a single tube from inlet header to outlet header. This increases mass velocity of flow and improves stability and temperature regulation of tubes. The bottom bends have holes. The bottom bend holes of the adjacent passes are connected with drain header by drain stubs. Each header serves to drain the adjacent tube passes and as equalizing header of pressure/flow. It will help to decrease multivaluedness and maldistribution of flow between parallel tubes of the module. Such design of HS noticeably decreases the corrosion of tubes.

What is claimed is: 
     
         1 . Heated surfaces (HS) with forced circulation of liquids/gases, comprising:
 a vertical multiple passage panel or serpentine coil comprising rows of vertical straight tubes with connections between them by top and bottom bends;   each bottom bend having a drain stub;   each drain stub being connected to a header; all headers are located below the bottom bends;   each header being connected to at least one bypass line for circulating water;   thus providing a stable operation of heat exchange elements of boilers and steam generators; wherein   each HS absorbing heat from exhaust gas.   
     
     
         2 . The heated surfaces of  claim 1 , wherein the drain stub is connected to the header, which is an elemental header; further comprising: at least one integral header receiving the bypass from the elemental header and outputting at least one drain pipe for water draining into a water accumulator. 
     
     
         3 . The heated surfaces of  claim 2 , further comprising drain stubs entering the integral header. 
     
     
         4 . The heated surfaces of  claim 2 , wherein the accumulator is located outside a casing; and the drain pipes go through the casing via holes. 
     
     
         5 . The heated surfaces of  claim 4 , wherein the holes in the casing have larger diameter than the drain pipes allowing thermal expansion of the drain pipe. 
     
     
         6 . The heated surfaces of  claim 2 , wherein both types of headers—integral and elemental serve as equalizers thus regulating a pressure and a flow liquid/vapor in parallel circuits. 
     
     
         7 . The heated surfaces of  claim 2 , wherein water always passes through the headers to cool down the bypass lines and the drain pipes. 
     
     
         8 . The heated surfaces of  claim 1 , wherein a diameter of the stub is smaller than a diameter of the bottom bend. 
     
     
         9 . The heated surfaces of  claim 1 , wherein a diameter of the stub is at least twice smaller than a diameter of the bottom bend. 
     
     
         10 . The heated surfaces of  claim 1 , further comprising: a drain box covering the bottom bends, the drain stubs, the drain pipes, the bypass lines and the headers; the box including water cooled wall tubes to keep proper temperature conditions in the drain box. 
     
     
         11 . The heated surfaces of  claim 1 , wherein each water cooled wall tube is connected to an inlet header and an outlet header. 
     
     
         12 . The heated surfaces of  claim 1 , wherein a pressure inside the panel or the coil is a subcritical pressure. 
     
     
         13 . The heated surfaces of  claim 1 , wherein a pressure inside the panel or the coil is a supercritical pressure. 
     
     
         14 . The heated surfaces according to  claim 1 , where the sizes of holes in the bottom bends and in the headers of multiple passage panels or serpentine coils are adjusted in such manner to have an equal pressure drop in all parallel circuits.