OCR Text |
Show conventional oxygen-gas 'bundle burner' is in excess of 10:1. There is no reason, provided the transport system will give a steady supply of pulverised fuel, why the oxygen-pulverised fuel burner will not give the same turndown. Some three years ago a prototype burner was manufactured and test fired at Air Products Limited, Crewe, to demonstrate the feasibility of replacing oxygen-natural gas firing with oxygen-pulverised fuel. The prototype burner would only allow a firing rate of 2.3 Mw, but demonstrated that a wide variety of pulverised fuels could be burnt using oxygen ranging from high volatile coals to low volatile cokes such as pet coke and coke breeze. Flame stability, flame profile and combustion efficiency were evaluated and, where necessary, minor modifications were made to the final burner design. Following the prototype burner development, the project was submitted for approval for an E.E.C. Grant which was awarded in 1987. Due to the nature of the oxygen-pulverised fuel firing and to ensure the maximum benefits are obtained, the pulverised fuel is transported to the burner via a Simon-Macawber dense phase transport system. The system uses a minimal amount of transport air and thus ensures that the oxygen-pulverised fuel flame temperature is not depressed by introducing large quantities of nitrogen. The burner has been developed to give dual fuel capabilities and can be fired on oxygen-natural gas or oxygen-pulverised fuel. The burner has been installed in a production furnace, and, to minimise the disruption to production whilst commissioning and development work was carried out, the burner can be switched from firing on pulverised fuel to natural gas at the press of a button. This has proved to be an extremely valuable commissioning tool - oxygen-natural gas firing has been selected whilst modifications have been made to the pulverised fuel transporting system maintaining the furnace heat input and enabling production targets to be met whilst still carrying out development work on the burner. As mentioned previously the burner is also capable of co-firing, i.e., firing with both pulverised fuel and natural gas. One phase of the E.E.C. Demonstration Project is the firing of the burner with alternative, cheaper, coal fuels. It has been shown that any combustible material will burn stably in an oxygen-fuel burner so the requirement for co-firing is not to ensure flame stability. The pulverised fuel transport system is designed for a maximum delivery rate of 650 kg/hr so, if a fuel of calorific value less than 29 MJ/kg ;s used, the desired heat input to the furnace cannot be maintained by firing on solely oxygen-pulverised fuel. When this situation arises the burner ;s fired in the oxygen-gas-pulverised fuel mode and the necessary additional heat input is given by the natural gas. Although the burner has the duel and co-firing abilities its normal mode of operation ;s envisaged to be oxygen-pulverised fuel. The Air Products bundle burner design enables the flame shape to be altered from a loose flame to a tighter 'pencil' shaped flame by Page 4 |