Document n9JJpBJRk7rVzmQo25EMMBXGz

I: Recommended Procedure lor Forced Shutdown Pulverized mat, oil, got 1. Shat ell the lire ImaoedloUljr 2. Shut down the forced draft 3. Clete cH the iteom eatpet 4. Stop the (lev of feedwater to boiler 4. Reduce air flew oi lew ai peuJble to a point conthtent with eafety Irani water or steam Mowing Into boiler room Stoker firing 1. Shut down the loel feed 2. Cat off the cembestboralr supply 3. la eil'eme emergency, smother fire. Take corn net to ceau get etplesbn * 4. Close off tho steam output 5. Xoep the feedwater flowing te oeletele the wafer level II: fcwedwe In Feed Uat Stoker firing 1. Cut lira* vfcsn the voter Iml drop of light >. 2. Clou oil blovdown end drain velvet b, coowm HiO j 1. Roduce loed on ftram turbtnss, stc m 4. Trip out rurblno If tko bellrr prvtnn' Faffs bslov 20% of eormef ;j e bodpr gn the line from purely operat ing cause* are (l) sudden cooling following the lose of a boiler lube (2) a large pressure drop produced by ex tinguishing the fires -without immedi ately shutting off steam outlet to the plant load. Thermal stress from chemical feed connections or cold-water inlets to the drum are problems of design that re quire thermo] sleeves for (heir correc tion. Operating Precaution. Mow that we know just how temperature stress can develop In a boiler drum w appreciate the value of an operating procedure that will provent any stress from de veloping. Briefly, abnormal stress does not develop if temperature differences between various sections of the dram are limited to (1) 100 F during pres sure-raising (2) 70 F during pressurereducing. These limits apply to drams of any thickness. In filling a boiler hold feedwater to SO F above or below drum temperature to reduce chances of tube seat leakage. Temperature difference can be mea sured by thermocouples, preferably spotted os follows: (1) on the thickest part of the drum, top and bottom (2) about 18 in. from the top on the drum circumference (3) on a boiler tube or circulating tube that is always at saturation temperature. An approxi mate check method for drums up to 10 In. thick U to hold tho' rate of In crease of saturation temperature to 100 F per hr so the drum porta will remain well within the temperature-difference limitation. For drams up to 4-in. thick ness (he restrictions on heating rates imposed by superheaters and other boiler elements hold drum temperature differentials within the recommended limits. Similarly on shutdown, unless it is accelerated by blowing down and feeding water, normal cooling rates at natural pressure drops lie well within the 70-F-per-hr limit For s thick-drum high-pressure installation, where steam can discharge into a lower-pressure sys tem, allow the pressure to drop with a reduced-firing rate, but hold to the 70F-pcr-hr temperature differential This may involve intermittent firing and com pletely filling the drum with feedwater, using thermocouples os a guide. Forced Shutdowns. Now let's look at forced shutdown!. A drum empty of water, but still under steam pressure, experiences serious stresses if relatively cold feedwater comes in contact with the drum surface. Any dram, thick or thin, can withstand a certain number of temperature shocks without damage. But no ona can predict just how many. Damage from such a shock far out weighs any temperature shock that could develop from the low heal given off by accumulated slag in a furnace selling. Because of this possibility, on operator's primary consideration should be safe-guarding the drum. Here is how he con do that. Tables I, II. A boiler fired with pulverised eo&l oil or gas and experiencing a tube rupture, say, should have Its fire cut off immediately, the forced draft shut down, and steam output closed off completely. In addition, stop the feed water flow to the boiler. With this pro cedure, by the time water within the drum has dropped to where furnacewall tubes are dry, heal emission from slag or .refractory will be so low that no damage will result. Air Aow should be reduced as low os possible: to a point where water or steam escoping from the tube rapture does not blow Into the boiler room. Once pressure in the unit hoe dropped, to sero follow the procedure for a normal shutdown. Do not empty the boiler system of water until the fur nace is cool enough to permit a man to enter. FuaUBsd Firing. With stoker or other fuel-burning methods whero the fire can't he killed Instantly, other steps must be taken. The problem resolves itself into a choice between risking damage to (1) drum by continuing thi flow of feedwater (2) furnace tula and boiler structure by shutting off thli flow. A majority of stoker-fired unit! are of lower pressure, end thus danger from quenching drum shells is not m prevalent. ^ For emergency, shut down the sup ply of fuel and combustion air. Smother the 6re by whatever means have bea; predetermined or are available withooii1! causing a gas explosion. Shut off atcso',1 output completely to prevent a sudden drop in pressure and temperstun1 within the boiler. \ Keep feedwater flowing to the cripy*-| pled boiler and try to maintain water level. Do not rob other boilers. Shut off supply entirely after fuel combo*-'' tlon drops to where overheating oT^ pressure parts will not develop---choul, A IS minutes'after the rupture has bees ' delected. From then on, the coolioi * procedure;follows that outlined for pul-.'.-, verized coal, oil or gas-fired units. - - if But suppose feedwater supply is lost.> If pressure parts remain intact, cut the'-;; fires out as soon as water level drops ^ out of eight. Conserve all water in the;^ boiler by dosing off blowdown eod jj drain. valves. Reduce the load ea ths'S turbines. This procedure prepares tbs 3 way-before pressure drop makes eo-.*,* pleto shutdown necessary. In addition" this method keep* safety valves frao blowing, end if feedwater is restored, eaves restarting the turbine. ~v If boiler pressure falls 20% belo^ normal, trip out tho turbine. It sav^ stress from temperature reductiec. throughout the boiler and turbine (talk; which could develop from abnormal; pressure drop. Onee feedwater supply is restored deliver water slowly into the* drum. } No reference has been made to op.', ersting pressures on this shutdown pij Hcedure. It bos been worked up marily for high-pressure thlck-druo i*' stallalions but applies equally to lo*t pressure thin drums. M (4761 POWER Auquil AUTOMATIC RELEASE, Kaot-operated, sends carbon dioxide DISCHARGE NOZZLES ore placed at Intervals along the pipefrom obove cylinders to discharge nozzles In vault on floor below tine, encircling room. Fire causes carbon dtoxkfe to flood room Automatic Electrical-Fire Textilo-plant circuit breaker and battery room protected again,t fire by a carbon-di oxide extinguishing -system By S O FRECIC Manager, Industrial O/vision Walter Kldda A Co fnc * Continuous MAiruPAcronmc at the Csrfield, N. J. plaqi of. the Foratmsnn wooletv Co la totally dependent on un interrupted electrical output from Its power house, which has a capacity of '300 kw. Recently the company intailed tn automatic carbon-dioxide fireprotection system, which prevents serf4us damage and costly electrical-power nterrupUgn by safeguarding the clrfu 1 breaker and emergency lighting tlery vault on the etaiion's ground J"d,bawr is the supply center f< K "ur * c^rcu*ta in the mony plai It U 107x1$ ft, end has sto firedoon--one at each end and two along one side- Fire-Protection Equipment. Directly above the breaker room, on the operat ing floor of the power plant, are 28 steel cylinders, each containing SO tb of liquid carbon dioxide. They ora manifolded together for simultaneous discharge fa case of fire. The cylinder manifold is connected by simple piping to a series ol 20 wide-dispersal dis charge nozzles, strategically located along the inside walls of the circuitbreaker vault Near the ceiting of the enclosed vault and directly over the breaker units are three heat actuators for detection of excessive temperature rise. They would quickly detect fire in any of the break ers. Automatically operating the cyl inder manifold valves, the heat actua tors release carbon dioxide through the piping network via discharge nozzles into the vault. How Equipment Operate*. The car bon dioxide provides its own propellent power, as it is stored In cylinders under BSO-psi pressure. When this liquid reaches the discharge nozzles and hits the air, it lures into a gas expanding to 450 times Its- stored volume. Slightly heavier than air, this cloud of gas and dry-ice snow floods the entire fire space, penetrating to every nook and corner of the circuit-breaker vault This reduces the air's normal oxygen con tent to below the point where combus tion can be supported. Elapsed time between outbreak of fire in the vault and complete extinguishment is only a matter of seconds. In fact the fire might be out before power-plant at tendants even detect it. At the main door to the circuitbreaker room, which would be closed automatically by a release valve actu ated by the discharging gas, ore two remote-control break-glass boxes for fire-emergency use. One is for manual cylinder release, used when the system Is taken off automatic operation. Man ual operation of the fire-protective sys tem is used when maintenance men ore working in the vault. Thus they have a chance to leave during a fire before carbon-dioxide gas is released. The other remote-control box sets off the power-house fire alarm, ringing four gongs at various points on tho Boor. After the fire Is extinguished, there is little cleaning-up to be done since car bon dioxide leeves no messy residue. CO* will not damage delicate electrical equipment or machinery. *owr-g August 1948 |477) W