Explosion Hazards in the Chemical Industry T H E O D O R E A . C O H E N , Wheelco Instruments Co., Chicago, III.
EXPLOSIONS in direct-fired processing kettles, boilers, industrial furnaces, ovens, kilns, and dryers remain one of industry's most serious hazards. An explosion may involve injury and death to
. T !$S® S
particularly in. gas-fired units. Fuel may leak past valves in the fuel line, t o accumulate in the combustion chamber where a n explosion may result on insertion of the lighting torch or upon ignition of the pilot burner. Unburned oil or pulverized coal may accumulate in the combustion chamber, and the gas distilled from it, upon mixing with air, may produce an explosive mixture that can be ignited during lighting. Ignition may be accidentally lost with decrease in fuel feed or stoppage of fuel, and fuel feed resumed without repeating t h e proper lighting cycle. A part of the equipment may maintain sufficient heat for a short time to ignite the fuel and provide a n explosion. With a decrease in air supply unburned fuel may accumulate in furnace orfluesand ignite when proper fuel-air ratio is restored, or there may be normal excess air.
Explosions with electrically fired equipment nave occurred in industrial drying ovens where solvent vapors are given off in the drying process. Records of one underwriting organization show 44 oil-fired explosions, 13 gasfired explosions, and 12 pulverized coal explosions in all classes of direct-fired equipment during a given period—45 per cent owing to lack of burner safeguarding or of flame-failure safety equipment; 3 5 per cent to defective burner operation, including clogging; 8 per cent to poor burner maintenance; and 3 per cent to distribution deficiencies. N o direct-fired processing kettle, oven, furnace, or boiler with an enclosed combustion chamber or a work chamber in which fuel gases may collect is immune from possible explosion hazards. The greatest number of explosions in industrial equipment occur during starting,
Figure 1. employees, physical damage to equipment, breakdown in production, and disablement of plant and equipment by fire. The production speedup occasioned by the war program has often transferred to new hands the responsibilities for tending equipment in which explosion hazards exist. To provide permanent protection againt loss of life and shutdown of plant, combustion safety equipment is being relied upon more and more to remove the explosion hazard. Present-day combustion safety equipment has proved more trustworthy than the human operator in preventing explosions, at a fraction of the cost of the equipment and plant given protection. Gaseous fuels are sometimes considered of greatest potential hazard from an explosion standpoint. Coal- and oil-fired equipment is not to be disregarded, as gases distilled from these fuels in a hot combustion chamber present a serious hazard. 302
'•-••
••·•
'ill."',·.·-
'
"
r.
-•
1 M "
r
'
'
O"
•
'
Figure 2. CHEMICAL
AND
ENGINEERING
NEWS
tion pilot burners through ignition transformers. When the pilot flames touch the flame electrodes, the instruments open the main solenoid valve and the main burners are ignited by the pilot burners. Upon flame failure at any of the burners, the main valve and pilot valve close aud the alarm bell rings.
Prevention of Explosions fe...flr-Ri'..·:-\
••·•••
Explosions cannot occur: 1. If the furnace, oven, kettle, or dryer has been purged of «11 fuel or hazardous vapors 2. If, after purging, an ample igniting flame from torch or some other source is properly applied to each burner before fuel is turned on 3. If air velocity at each burner is kept sufficiently low to prevent loss of ignition in starting 4. If fuel is sufficiently rich to ensure immediate ignition from torch 5. If, after ignition is established, there is proper mixture of fuel and air throughout the entire furnace operation, and stable ignition is maintained at all operation rates. Similarly, after starting, explosions cannot occur: 1. If stable ignition has been attained 2. If a flame failure at burner causes an instantaneous shutdown of fuel supply 3. If a power failure to burner equipment causes an immediate shutdown in fuel supply 4. If a reduction or failure in air or fuel supply causes an immediate shutdown in fuel supply control means. Proper consideration of all factors contributing to combustion explosions points to the necessity of thorough purging of the combustion chamber before lighting, and of adequate flame-failure safety protection equipment. Purging is usually accomplished by means of an air flow switch in combination with a time delay relay that together supervise operation of a ventilating fan. A flame-failure safety device must cut off the fuel supply to a burner in case of flame failure or loss of ignition, and must provide the cut-off quickly to prevent raw fuel from entering the combustion chamber after the flame failure has occurred. Early flame-failure devices fall into two general classes, both making use of heat radiated from the flame. One type employed a heat-sensitive member, such as a thermostatic strip or a thermometric bulb with an expansible liquid. Another type employed a thermocouple. In operation, sources of heat other than the flame sometimes impinged upon the thermally sensitive members and maintained the fuel supply valves open for a considerable length of time after flame failure. To overcome these objections, the ability of a flame to conduct an electric current has been employed in a modern combustion safeguard instrument. An electrode is introduced into the flame and connected to the instrument, which reacts in accordance with the amount of resistance in its electrical circuit, of which the flame is a part. The resistance remains within certain limits as long as a flame is in contact with the electrode, and the instrument holds open valves in the burner fuel line and maintains combustion· Flame failure, however, increases the resistance, and .the instrument instantly closes the
VOLUME
21, NO. 5 » »
Figure 3 shows a combustion safeguard hookup for oil or pulverized coal burning systems.
Figure 3.
fuel valves to prevent flow of fuel to an unignited burner. When a burner is being ignited, a pilot light, also in the circuit and in contact with the electrode, provides the necessary resistance to enable the instrument to open fuel lines to the burner. For use with fuels other than gas, which burn with luminous flames, a device incorporating a photoelectric cell is employed in place of the electrode. Modern combustion safeguard instruments; after shutting both main and pilot valves upon flame failure, provide a time delay for purging the chamber of combustible gases before lighting is permitted. An assurance against explosions resulting from failure of any part of a modern combustion safeguard instrument or a short in the circuit is provided, as the device then closes fuel valves as in case of flame failure. Figure 1 illustrates a hookup for gas fuel with provision for controlled purging of the combustion chamber. No ignition attempts can be made until the airflowswitch and the time delay relay indicate that the combustion chamber has been purged of all combustible vapors. When purging is completed, the instrument opens the solenoid pilot valve and turna on the ignition spark The gas from thev pilot burner is ignited by the spark, and the circuit is completed when the pilot flame comes in contact with the electrode. The main solenoid valve is then opened, allowing fuel flow through the manual control valve to the main burner, where the gas is ignited by the pilot flame. After a fixed time cycle, the spark ignition and the pilot burner are shut off. If, for any reason, the pilot burner does not light, or if the main burner fails to ignite from the pilot, the instrument immediately shuts off the pilot and main fuel valves and sounds the alarm. A flame failure during operation also shuts down the burners instantly, and, after a purging period determined by the instrument and set in accordance to the need of the equipment protected, causes a relight cycle. Figure 2 shows how a multiple-burner gas-fired dryer, oven, or furnace may be equipped with combustion safeguards. Depression of the push button opens the pilot valve and energizes all spark igni-
* MARCH
10,
1943
After a purging period, during which the hand torch cannot be ignited, the hand torch solenoid valve is automatically opened. The manual valve on the torch may then be opened and the torch ignited. When the torch is inserted through t h e lighting port so that the flame touches the electrode, the instrument opens the main fuel valve. No oil or pulverized coal can reach the burner until a flame is present -to ignite it, and no flame can be introduced into the combustion chamber until the chamber has been purged of all accumulated combustible vapors. The hand torch is withdrawn from the chamber after lighting, and its manual valve closed. If the fuel has been successfully ignited* the photoelectric cell will react to cause the instrument to keep the fuel valve open. I f ignition is unsuccessful, t h e valve will be shut down and the alarm bell will ring. A flame failure during t h e operating period causes an instant fuel shutdown, sounding the alarm bell.
Figure 4.
The combustion safeguard hookup for oil or pulverized coal burning equipment shown in Figure 4 incorporates a controller, which may be either a pressurestat or a thermostat. A demand for heat by the controller is transmitted to the instrument., which turns on the spark ignition and pilot burner. When the pilot Tight strikes the electrode, completing the circuit, the main fuel valve is opened and oil or pulverized coal admitted t o the combustion chamber where it is ignited by the pilot flame. After a fixed time period, tne pilot and ignition are shut off. If tne ignition cycle has been satisfactorily completed and the main fuel flame established, the fuel safety valve stays open, held in that position by the photoelectric cell, and the instrument ignition control assembly resets itself, automatically, for a new lighting cycle when required. In the case of flame failure after the ignition period, the main fuel valve is instantly shut off, and a new lighting cycle takes place.. 303
THE Niagara Falls plant of The Mathies o n Alkali Works (Inc.) has been presented with the Army-Navy Produc tion Award for high achievement in the production of chlorine, synthetic ammonia, caustic soda, high test calcium hypochlo rite, sodium chlorite, sodium methylate, and other chemicals that are vitally needed for t h e nation's war effort. T h e "E" flag, which symbolizes the award, was presented o n Feb. 26 by Col. Harry A. Kuhn, of the Office of the Chief, Chemical Warfare Service, Washington, D. C , and was accepted by G. W. Dolan, executive vice president of the Mathieson organization. Col. Kuhn was introduced by L-fc. Col. Charles F. Mosher, Officer-inCharge of t h e Buffalo Sub-Office, Roches ter Ordnance District, representing Col. F. J. At wood, of the District. Master of Ceremonies was M. F. Keogh, General Counsel for The Mathieson Alkali Works. " E " pins were presented by Lt. Comdr. George W. Eighmy, U. S. N. R., of Buffalo, to a committee representing the plant em ployees, whose members were Frank A. Sweet, Chairman, George Allinson, and Jacob Gessner, and to F . B. Butler, Man ager o f Mathieson's Niagara Operations. In His presentation address, Col. Kuhn pointed out that the chemicals used in making war materials and for preserving the health of our armed forces are just as important for winning battles as the highexplosive shells that blast the enemy out of their rat holes. E. B. Badger & Sons Co. Brigadier General Leslie D . Groves, Deputy Chief of Construction Division, Office, Chief of Engineers, Washington, D. C - , presented the Army-Navy Award for excellence in war construction t o the employees of Ε. Β . Badger & Sons Com pany a t the West Virginia Ordnance Works, Point Pleasant, W. Va., on March 4. The award is especially interesting in that it was presented for excellence in construction. E. IB. Badger, president of the centuryold Boston engineering firm which bears his name, replied t o General Groves fol lowing the presentation of the Army-Navy "E" pennant. Individual " E " lapel pins were given t o approximately 1,500 workers from West Virginia and nearby Ohio.
Elliott Company The Jeannette Plant of the Elliott Com pany w a s awarded the coveted Army-Navy Production Award on Feb. 5, recognizing exceptional performance in supplying war material for America's fighting forces.
The Ohio Injector Company The Ohio Injector Company of Wads•worth, first member of t h e valve industry "to receive t h e Army-Navy " E " award and pennant for high achievement in the pro duction of war goods, has wpn additional
304
must have to bring this war t o a successful conclusion."
Du Pont Co.
N C L U D E D in t h e list of companies recently receiving Army-Navy " E " Production Awards were:
Î
Babcock & W i l c o x Tube Co., Beaver Falls, Penna., plant E. B. Badger & Sons, Boston, West Virginia Ordnance Works S. F. Bowser & Company, Fort W a y n e (a star) Consolidated Chemical Industries, Inc., Baton Rouge Cook Paint & Varnish Co., North Kansas C i t y , M o . Davis Emergency Equipment Co., Inc., Newark E. I. du Pont de Nemours & C o . , Inc. (three plants) Elliott Company, Jeannette, Penna. B. F. Goodrich C o . (two plants) Goslin-Birmingham M f g . C o . , Bir mingham, A l a . I L G Electric Ventilating Co., Chicago Mathieson A l k a l i Works, Niagara
Falls The O h i o Injector Company, Wadsworth (a star) Republic Steel Corp., Cleveland Reichhold Chemicals, I n c . , Detroit (a star) Sharpe & Dohme (two plants) Std. O i l Development C o . , Bayway, N . J. Worthington Pump & Machinery Corp., Buffalo Maritime " M " Edward V a l v e & Chicago, Ind.
Mfg.
Co.,
East
honors according to announcement by t h e N a v y Board of Production Awards at Washington. I n announcing the new honors, Admiral C. C. Bloch, U . S. N . , retired, Chairman of the N a v y Board for Production Awards, in a letter to Wayne Young, president of T h e Ohio Injector Company, stated: "I congratulate each a n d every one of the employees of T h e Ohio Injector Com pany upon their continued splendid achievement i n outstanding production. This award is difficult to win in the first instance and t h e requirements for renewal are equally exacting. B y winning t h i s additional honor y o u all have demon strated a solid determination to supply our fighting forces with the materials t h e y
CHEMICAL
On Feb. 25 Major General Clifford L . Corbin, Acting Quartermaster General o f the United States A r m y , presented t h e Army-Navy " E " flag ix> the D y e Works Associated Units of E . I. d u P o n t d e Nemourj & Co., Deepwater Point, N. J . Captain C. G. Mayo, U. S. N . , District Supply Officer, Fourtb. Naval District, presented the " E " p i n s to the employees. W. S. Carpenter, Jr., president of t h e company spoke a t the ceremony. "Now we are involved in the biggest game of all; t h e stakes are enormous, w e can't afford to lose. A. great big job has been done by y o u and done successfully. This has been recognized by our Armed Forces, and t h e y h a v e sent their repre sentatives here today t o decorate y o u . I believe that you will s a y that I speak for you w h e n I assure t h e s e gentlemen that, while we very greatly- appreciate their recognition of your efforts, no one appreci ates better than you tfcat there i s much yet left to be done. I believe w e can assure them t h a t it is going to b e done and t h a t when this job is finished w e will roll on t o the next one, contributing again to the peacetime economy of the country and, incidentally, keep ourselves i n readi ness should another disturber of t h e peace of the world threaten oixr homeland." Colonel Ε. Ε . Gesler of t h e Office of Chief of Engineers in Washington pre sented the A r m y - N a v y "E" flag t o em ployees of the construction division of D u Pont, who built the W a b a s h River Ord nance Works, at a ceremony o n March 3 . Captain G. P. Kraker, Commanding Officer a t the U. S. N a v a l Ordnance Plant, Indianapolis, presented the " E " pins t o the employees.
Other Awards Coveted A r m y - N a v y "E" Award em blems were conferred u p o n several hundred employees of the ILG Electric Ventilating Co., Chicago, 111., during impressive "between-shift" ceremonies at Rockford, 111., o n Feb. 11. The award flag w a s presented b y Lt. Comdr. T . H. Urdahl, U . S. N . R., Bureau of Ships, Washington F a n and Blower Division, and -was accepted b y John M . Frank, president of the com pany. Major Lauris E e k of the U. S. Army Air Force, Chicago, presented the pins t o employees. L t . Alexander B . Maley, U . S. N. R., N a v y Public Relations, Chicago, served as m a s t e r of ceremonies. The Maritime "M" pennant and labor merit insignia, highest production honors of the United States Maritime Commission have been awarded to t t i e Edward Valve & Mfg. Co., Inc., East Chicago, Ind., and will be presented on M a r c h 13. T h e com pany h a s been building cast and forged steel valves for Maritime Commission ships since 1938.
AND
ENGINEERING
NEWS
'L·
Lt. Comdr. G . W . Eighmy, U . S . N . R., presents M E " p i n to Frank A . Sweet, chairman θ ί Plan* Employee Committee, Niagara Falls plant, Mathieson A l k a l i Works, Inc., at the presentation ceremonies on Feb. 2 6 . Left ttf right. G . W . Dolan, F. B. Butler, M . F. Keogh, and Col. Harry A . Kuhn.
C. Η . Doherty, Jr., works manager; Lammot du Pont, «hairnuin of Board of Directors; and Governor M . M . Neely of W e s t Virginia at presentation of A r m y - N a v y 4 Έ " to Belle Works, E.l.du Pont d e Nemours Λ C o . , Jan. 14. \-jf~-
*ψΜ **Λ/
,
A n official group of A r m y and Navy men inspectthe Jeannette plant of Elliott C o . which recently won the " E " in recognition of its production record.
€^
^ V '$:.: •;..53^,
tf-p?
^H
A . G . Pratt, president, and P. D . White, vice president and general manager, of the Babcock & Wilcox Tube Co. hold " E " burgee received at A r m y N a v y " E " award ceremony, Feb. 4 et the Beaver Falls, Penna., plant. A t M r . Pratt's right is Rear Admiral W . C. Watts, who presented the flag.
Γ\Γ\ίνΠ 'fj>
:
*w
- y
~'\ > •a-' zty. ~'J-'\i
-'..'- "• t
£
, , _
'.:-/:-. *. * • - " -
A r m y - N a v y M E " was awarded to Crane Co. in a recent presentation at the Chicago Works. Left to right. Estelle Maslowski; Rear Admiral Clark H . W o o d w a r d ; J . H . Collier, president; H . H . Upton/ and C o l . J, F. Butler. Mrs. M i n n i e Schuster is congratulated u p o n receiving the " E " emblem during A r m y - N a v y " E " award ceremonies at I L.G Electric Ventilating Co., Chicago. Left to right. ILfl -:
*^F- _,-
ΐ „
