Patent GB-883508-A (GB)
Title: Electrically operated stove changing control apparatus for blast furnaces
Inventor: BRAUN WILLI
IPC: F16K31/02
Filed: 1960-01-06
Abstract: 883,508. Control of several motors. ZIMMERMANN & JANSEN G.m.b.H. Jan. 6. 1960, No. 639/60. Class 38 (3). [Also in Group XIII]  In a blast furnace installation in which' air for the furnace is heated in a plurality, of hot blast stoves HBS1, HBS2 and HBS3, each stove is  provided with a hot blast valve HBV, a  cold blast valve CBV, at least one chimney valve CVI or CVII, a burner shot-off valve BV, and a gas shut-off valve GV, and electrical control means are adapted to provide a predetermined sequence of operation of the valves for each of the stoves. The valve-changing sequence is initiated by a single manually-operated selector switch, included in a control panel (not shown), associated with each stove. An electrical interlock ensures that one of the stoves is always on blast and prevents a stove being switched to the " on gas " condition before another stove has been switched to the " on blast " condition. The interlock switch may be disengaged from the circuit when, e.g. all of the stoves are to be closed down. A safety cut-out switch operates during operation of the selector switch handle. The valves are each actuated by a motor drive and limit switches are associated with each valve. Provision is made for manually operating any one of the valves, an electrical cutout then being operative (Fig. 10, not shown). In Fig. 1, the stove HBS1 is on blast, i.e. supplying hot air to the blast furnace BF, the stove HBS1 is on gas, i.e. the checker work therein is being heated by gases from the burner 30, and the stove HBS3 is inoperative. Combustion air is supplied to the burner 30 through a duet 38 by a fan 36. A duct 50 supplies air under the control of a butterfly valve (not shown) from the cold blast main 48 to the hot blast stream in order to control the temperature of the blast entering the furnace. Each of the stoves shown is provided with two chimney valves CVI and CVII. The chimney valve CVII and also the cold blast inlet valve CBV are provided with small pilot valves which are opened immediately before the valves CVI and II and CBW are operated, this being necessary to prevent a sudden change in pressure in the stove when changing from the " on gas " to " on blast " condition and vice versa. When the furnace is to be shut down, provision is made for burning the residual gases therefrom in one of the stoves rreferably one which has been on gas and is therefore hot. This operation, termed "backdrafting" " is effected by a separate switch on the control panel which closes all the valves except the cold blast inlet. This permits residual gases from the furnace to flow back into the stove where they are burned, the burner gas valve being throttled so that the burner operates with sufficient excess air to burn the residual gases. Whilst backdrafting is going on, the remaining stoves are maintained in a " stove-bottled " position that is any valves on these stoves which were open when backdrafting is commenced, are closed. The " stove bottled " condition is initiated by an appropriate movement of the selector switch on the control panel to a position which closes the remaining valves from the " on gas " or " on blast " conditions. Operation of the control selector switch to the " on gas " position results in (a) closure of hot blast valve HBV, (b) closure of cold blast valve CBV, (c) opening of pilot valve 136 (see Figs. 11, 12), in chimney valve CVII, followed by opening of chimney valve CVII, (d) opening of chimney valve CVI, (e) opening of burner shut-off valve BV, (f) opening of gas shut-off valve GV. The opening of the gas shut-off valve results in a complete de-energization of the circuit. Operation of the control selector switch to the " on blast " position results in (a) closure of the gas shut-off valve GV, (b) closure of the burner shut-off valve BV, (c) closure of the chimney valve CVI, (d) closure of the chimney valve CVIII, (e) opening of the pilot valve (not shown) associated with the cold blast to raise stove pressure to that of the cold blast, (f) opening of the cold blast valve CBV, (g) opening of the hot blast valve HBV. When changing a stove from " on blast " to " bottled," the control selector switch is turned to " bottled up from blast " position and this results in a closure of hot blast valve, followed by a closure of cold blast valve, all other valves having been previously closed in the " on blast" condition. Normally (due to stove interlock switch) a stove cannot be set to " bottled up from blast " unless one of the other stoves is supplying hot blast to the furnace (BF). When necessary, however, e.g. on shut-down of the furnace, the interlock switch may be operated to enable the stove to set to " bottled up from blast." When changing a stove from " on gas " to " bottled," the selector switch is turned to the " bottled from gas " position which results in (a) closure of the gas shut-off valve GV, (b) closure of the burner " shut-off " valve BV, (c) closure of the chimney valve CVI, (d) closure of the chimney valve CVII, all other valves, i.e. the cold blast and hot blast valves remaining closed.