Velox boiler

Velox boiler
Velox steam generator installed at Blin and Blin
Classification	Turbo steam generator
Application	Mostly used for electrical generation
Fuel source	Fuel oil
Components	Axial compressor Combustion chamber Fluegas turbine
Inventor	Brown Boveri Company (BBC)
Invented	1931

AVelox boileris aturbocharged,forced circulation,water-tube boilerwhich utilises anaxial flow compressorand agas turbine.Velox (Latin: "fast" ) boilers, also known as Velox steam generators, were developed in the early 1930s by theBrown Boveri Company (BBC)of Switzerland.Velox boilers were the first commercially available machines to make use of axial compressors and played a pivotal role in the later development of BBC’s industrial gas turbines.

Design

Velox principle

From Brown Boveri Review

The Velox principle combines the use of combustion under pressure, with very high flue gas velocities and with a gas turbine, whereby the pressure in the combustion chamber, the high gas velocities and the pressure drop of the gases for production of work are created by means of a compressor driven by the gas turbine, the latter being actuated by the products of combustion.

The great significance of the Velox idea lies in the fact that by means of the increase in pressure and velocities the components are greatly reduced in size, and the processes are accelerated without impairing the efficiency.

Working

Diagram showing the main components of a quick-acting stand-by power plant with a Velox steam generator.

In a Velox steam generator used for electrical generation, flue gases from the combustion chamber are used to turn a gas turbine which is connected to a compressor which together make up the charging set. The compressor increases the flow of hot air which increases the rate of heat transfer to the water in the boiler tubes causing more steam to generate. The steam is used to turn a steam turbine which is coupled to an electrical generator.

The combustion chamber of the Velox could produce flue gasses by burningfuel gassesorheavy fuel oil.Blast furnace gaswas typically used as fuel by Velox sets installed insteel mills.Efficiency of Velox steam generators was generally around 88—90% when burning blast furnace gas and 91—93% per cent with fuel oil. Such efficiencies were maintained from 25 to 100% of load.

History

Prior toWorld War I,BBC had worked on a number of experimental gas turbine projects addition to their commercially successful steam turbine business. BBC's gas turbine collaborations included those ofHans Holzwarth,Armengaud-LemaleandAuguste Rateau.BBC had also done experimental work on atwo-strokeversion ofHerbert Humphrey’sHumphrey pumpwhich would have been used for power generation (a so called "wet gas turbine" ). None of these early gas turbine experiments produced a commercially viable product.

From 1927, BBC again collaborated with Hans Holzwarth on a two-stage constant volume explosion gas turbine. The performance of the Holzwarth turbines ultimately did not meet expectations with a major issue being the loss of heat through the water jacketing. It was recognised that the loss of heat into the water jacket could be turned into an advantage by using the heat in a turbocharged boiler. Based on these observations, and existing competencies with turbochargers and steam turbines, BBC developed a constant flow gas-turbine compressor set for use in steam turbines which became the Velox boiler.

Two Velox steam generators on the test bed at BBC works in Baden, Switzerland

The first Velox boiler was exhibited at theVDIconference in Berlin during 1931. Orders quickly followed with the first being for theMondevillesteelworks inNormandy,France during 1932.A total of 110 Velox Boilers were built with 75 of these being ordered during the 1930s.

SS Bore II. The first vessel to be exclusively equipped with Velox boilers.

The vast majority of Velox boilers were used for electrical generation. In power stations Velox boilers were valued for their rapid starting times and compact size. Velox boilers were also built for ships and railway locomotives however they never found widespread use in these applications. In 1939, BBC delivered a single Velox boiler to the BritishRoyal Aircraft EstablishmentinFarnboroughfor evaluation and testing.

Experiments with coal fuel were conducted by BBC in an attempt to increase sales of Velox boilers beyond customers with gaseous and liquid fuels.Pulverised coal,fed into the Velox combustion chamber by compressed air, was tried but caused excessive erosion on the gas turbine from flying ash particles.

The development of the Velox steam generator lead directly to the development of the first industrial gas turbines. In 1936, BBC built the world’s first constant flow industrial gas turbine for theSun Oilrefinery inMarcus Hook, Pennsylvania.The early BBC gas turbines were essentially Velox boilers with the steam component removed. The Marcus Hook compressor turbine set was used for the catalyst regeneration cycle of theHoundryoil refining process and included a 900 kW alternator coupled to the set's gas turbine. Experience with Houndry gas turbines lead to BBC’s development of theworld's first gas turbine power station built at Neuchâtel,Switzerland.