Premixing Apparatus

Abstract

A premixing apparatus has: a butterfly valve and a changeover valve for changing over, between high and low, a ventilation resistance in an air supply passage and in a gas supply passage, respectively; and an interlocking mechanism to open or close the changeover valve in interlocking with the opening or closing of the butterfly valve. In either of the small-capacity state in which the ventilation resistance in the air supply passage and in the gas supply passage is made high to attain a small-capacity state or in a large-capacity state to attain a large-capacity state, adjustments are arranged to be made to make appropriate the excess air ratio of the air-fuel mixture. An interlocking mechanism is constituted: to maintain the changeover valve in a fully-closed state when the butterfly valve lies in a predetermined first rotation angle range inclusive of the closed posture; and to maintain the changeover valve in a fully-opened state when the butterfly valve lies in a predetermined second rotation angle range inclusive of the opened posture. The rotation angle of the butterfly valve at which the excess air ratio of the air-fuel mixture becomes the predetermined appropriate value within the first rotation angle range is set to a closing-side stop angle of the butterfly valve. The rotation angle of the butterfly valve at which the excess air ratio of the air-fuel mixture becomes the predetermined appropriate value within the second rotation angle range is set to an opening-side stop angle of the butterfly valve.

Description

TECHNICAL FIELD[0001]The present invention relates to a premixing apparatus for mixing fuel gas with air to supply thus obtained air-fuel mixture, through a fan, to a burner.BACKGROUND ART[0002]As this kind of premixing apparatus, the following is known in Patent Document 1, i.e., JP-A-2015-230113; that is, a downstream end of that gas supply passage for supplying fuel gas which has interposed therein a flow control valve, is connected to a gas suction section disposed in an air supply passage on an upstream side of the fan. The premixing apparatus comprises: an air resistance changeover means for changing over, between high and low, a ventilation resistance in that section of the air supply passage which is on an upstream side of the gas suction section; and a gas resistance changeover means for changing over, between high and low, a ventilation resistance in that section of the gas supply passage which is on the downstream side of the flow control valve.[0003]By the way, in case a...

AI Technical Summary

Benefits of technology

The technical effect of this patent is to improve the efficiency and reliability of ignition in a burner system by performing ignition in a state where the excess air ratio of the air-fuel mixture is low and the state is gas-rich, which prevents ignition failure. This is achieved by rotating the butterfly valve to the closed posture when the burner is ready to be ignited.

Problems solved by technology

However, in case the required combustion amount falls below a predetermined value and, as a result, the rotation speed of the fan falls below a lower limit rotation speed below which the proportional characteristics of the air supply amount cannot be maintained, or in case the electric current to the proportional valve (electric current to be charged to the proportional valve) has fallen below a lower limit electric current below which the proportional characteristics of the gas supply amount cannot be maintained, the air or fuel gas in amount depending on the required combustion amount can no longer be supplied.

Also in this arrangement, if the fan revolution has fallen below a lower limit revolution at which the proportional characteristics of the air supply amount can be maintained, the air or fuel gas depending on the required fuel amount can no longer be supplied.

Further, only by increasing the ventilation resistance in the air supply passage, the amount of fuel gas supply will exceed the amount corresponding to the required combustion amount due to an increase in the negative pressure in the air supply passage.

However, for that purpose, it becomes necessary to replace the related parts in the air supply passage, thereby requiring a considerable cost.

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