Circuit assembly for once-through steam generators

Abstract

A once-through steam generator or boiler of simple modular construction that utilizes vertical heat transfer tubes, intended primarily for heat recovery in combined cycles. It utilizes a novel method of assembly and operation that make it particularly effective for large combined cycles. Circuit assemblies with a once-through flow path are the key building blocks used to assemble boilers to fit any size gas turbine. They are individually bench fabricated in a horizontal plane. The boiler is manufactured by sequentially stacking individual circuit assemblies in parallel thereby building a circuit module. During the stacking process the inlet and outlet of each circuit assembly are connected to headers to allow the modules to be erected into a heat transfer bundle. For large boilers several transportable circuit modules are interconnected in the field to complete a once-through boiler. Through the use of jumper tubes and a novel maintenance space integrated in the boiler, interconnection of modules in the field is simplified at installation and repair made easy. A novel method of dewatering and drying vertical tube boilers is incorporated. The dewatering method uses stored energy to reverse the flow of water and steam in the boiler thus forcing water out of the tubes. This operating method is important in preventing corrosion of carbon steel tubes, thereby permitting the practical application of carbon steel tubes to vertical tube once-through steam generators.