Question of the Month – 2018

Question of the Month for December 2018

QUESTION:

Worst Boiler Explosion You Remember Happened in December?

 

ANSWER:

Remembering the Malden Mills fire: 'A terrible night'

METHUEN — In the Merrimack Valley, many adults remember where they were and what they were doing the night Malden Mills, a textile manufacturer that at one time was Lawrence and Methuen’s largest employer, was devastated by a massive, wind-driven fire.

Exactly 20 years ago Friday, on Dec. 11, 1995, a boiler exploded in the Monomac or “flock” building around 8 p.m. and sparked an inferno that could be seen for miles around. About 300 employees were working that night, and more than three dozen of them were injured.

Ten of them suffered life-threatening injuries, according to Lawrence Fire Chief Brian Moriarty, who was among the first paramedics to respond.

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Surprisingly – some would say miraculously – the fire did not claim any lives that night.

About 200 firefighters from across Massachusetts and New Hampshire came to Lawrence to help crews battle raging 50-foot flames on the 29-acre property.

First on the scene were Methuen firefighters, some of whom are still with the department – including the new chief, Tim Sheehy.

“I was at home,” recalled Lt. Scott Sullivan, now in his 24th year as a Methuen firefighter.

Kenneth Bourassa, the chief at that time, issued the order: “Send everybody.”

Sullivan went to Malden Mills in a spare pump truck, along with Lt. William Barry, now the assistant chief, and Dennis Fragala, a deputy chief who will soon retire after 32 years of service.

“We laid a feeder line to the ladder (truck),” Sullivan recalled. The Monomac building collapsed, however, and wiped out that line of hose.

So they drafted water from the nearby Spicket River. But most of the water that was poured on the flames that night came from city hydrants in Methuen and Lawrence.  Firefighters had to lay down hoses as far as 1,000 feet to hook up to those hydrants, recalled Capt. Michael Buote.

“It was cold that night,” Sullivan said. “It was the biggest fire I’ve ever seen.” He estimated that the flames reached 50 to 60 feet in the air.

The heat of the fire vaporized pigeons that headed into the burning buildings, looking for their roosting places, he said.

Dan Donahue, now a deputy chief, recalled that about an inch of snow had fallen the previous night. That amount of snow on roofs, he said, was enough to save many houses in the nearby Arlington District from burning down.

Donahue and other firefighters described the hundreds of burning embers that were falling from the conflagration. Some of those embers were as large as basketballs, they said.

None of the Methuen firefighters suffered serious injuries, but the department sustained a significant casualty: Ladder 1. The thick ice that built up on that truck destroyed it.

The ladder truck that replaced that apparatus will soon be replaced by a new one, Sheehy noted.

“Fire eats air,” Fragala pointed out. He and other firefighters saw an example of this phenomenon as debris from the streets, such as cigarette butts and pieces of paper, was sucked toward the inferno.

A gas line at Malden Mills ruptured – and because the line could not be shut off without cutting off service to the surrounding area, “we had to leave it burning,” Fragala said. Methuen had to keep a truck at the site of the flame until it burned out. he said.

Moriarty was working as a paramedic at Lawrence General Hospital at the time of the fire. He described one of the burn victims: “His skin was hanging down to his knees from both arms.”

He and his partner, James Murphy, now a Lynn fire lieutenant, set up a triage area in the security building. Along with other paramedics, including James Garrity, who is now a Methuen fire lieutenant, they arranged transportation of victims to hospitals, most by ambulance, some by helicopter.

 

Question of the Month for November 2018

QUESTION:

What is meant by Stoichiometric Combustion?

 

ANSWER:

Stoichiometric Combustion is the perfect combination of air and fuel that result in perfect combustion! Sounds good doesn’t it? Unfortunately, it is impossible to achieve in burners that you would commonly find on a boiler.

So why toss this term about? For the simple reason that it gives us a target in which we might compare our combustion conditions against. For example if we supply too little air, the burner will run “rich”. This means that not all the fuel was burned. Not only is this inefficient it also results in sooting that will decrease the heat transfer in the boiler.

Introduce too much air into the process and again, you reduce efficiencies. Not all the fuel is burned. This is why we strive for the perfect balance  – Stoichiometric Combustion.

 Stoichiometric Combustion

For a methane/oxygen flame the chemical reaction can be written:

CH4 + 2 O2 ? CO2 + 2 H2 O + Q

where Q is the heat of combustion. In this reaction, atoms are conserved and the equation balances for each of the species. The reaction is a stoichiometric reaction, and the coefficients multiplying each of the chemical species are known as the stoichiometric coefficients.

If air is used in the reaction rather than pure oxygen, the inert gas nitrogen will be present. Air is about 79% nitrogen by volume and 21% oxygen by volume. For a stoichiometric combustion reaction in this case each mole of oxygen will be accompanied by 3.76 moles of nitrogen. The reaction equation is then written:

CH4 + 2 O2 + 2(3.76 N2) ? CO2 + 2 H2 O + 2(3.76 N2) + Q

Question of the Month for October 2018

QUESTION:

Where Does Water Hammer Occur?

 

ANSWER:

Water hammer can occur in any steam or condensate line. Its effects can be even more pronounced in heterogeneous or condensate bi-phase systems. Condensate bi-phase systems contain two states, the liquid (condensate) and a vapor (flash or generated steam). The bi-phase condition exists in a steam system where condensate coexists with generated or flash steam. Typically examples include heat exchangers, tracer lines, steam mains, condensate return lines and sometimes, pump discharge lines.

A common example is water hammer occurring during the start-up or energizing of a steam main. If the steam line is energized too quickly and the condensate created during the startup is not being properly removed; water hammer will be the result.

Effects of Water Hammer

The effect of water hammer cannot be underestimated as its forces have been documented to result in many of the following:

  • Collapse the float elements in steam traps
  • Overstress pressure gauges
  • Bend internal system mechanisms
  • Crack steam trap bodies
  • Rupture pipe fittings
  • Cause valve failures
  • Cause heat exchanger equipment tube failures
  • Break pipe welds and even rupture piping systems
  • Failure of pipe supports.

Question of the Month for September 2018

QUESTION:

In order to determine the heating value of coal in BTU per pound, what is used?

 

ANSWER:

Ultimate Analysis – Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulphur, oxygen, nitrogen.

Ultimate analysis is also known as elemental analysis, it is the method to determine the Carbon, Hydrogen, Nitrogen, Sulphur and Oxygen content present in solid fuel.

Question of the Month for August 2018

QUESTION:

A volute is part of a:

a. centrifugal pump.

b. gear pump.

c. hose pump.

d. plunger pump.

ANSWER:

 a. centrifugal pump

Volutes are designed to capture the velocity of liquid as it enters the outermost diameter of an impeller and convert the velocity of the liquid into pressure.

In the picture below, notice that the impeller is not located in the center of the volute. This is intentional. The portion of the volute that extends closest to the impeller is called the cutwater.

Note that starting from the cutwater and proceeding in a counter-clockwise fashion, the distance between the volute and the impeller increases gradually. This has the effect of causing pressure to build within the volute as the distance increases. Once the point of greatest separation is reached – directly next to the cutwater moving in clockwise direction – the pressure is at its greatest, and water is forced out the casing when it encounters the cutwater.

 

Question of the Month for July 2018

QUESTION:

What is ductility?  What is malleability?  What is resiliency?

ANSWER:

Ductility = Ductility is when a solid material stretches under tensile stress. If ductile, a material may be stretched into a wire.

Malleability = Malleability, a similar property, is a material’s ability to deform under pressure (compressive stress). If malleable, a material may be flattened by hammering or rolling.

Resiliency = In material science, resilience is the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading.

Question of the Month for June 2018

QUESTION:

A boiler develops 5000 BHP.  The temperature of the feedwater entering the boiler is 225 deg. F and the enthalpy

of the steam leaving the boiler is 1200 Btu/lb.  How many pounds of steam per hour is this boile4r generating?

ANSWER:

W = BHP X Btu/BHP

         Hs – Tfw -32

 

W = pounds of steam/hr

BHP = Boiler horsepower

Hs = heat per pound

Tfw = Feedwater temperature

 

Btu/BHP = 33,475

W = 5000 X 33,475

         1200 -(225-32)

Answer (W = 166,211.5 lb/hr)

 

Question of the Month for May 2018

QUESTION:

What materials are used in the construction of water columns?

ANSWER:

Water columns are made of cast iron, malleable iron, or steel.  According to the ASME Code, cast iron can be used for pressures up to 250 psi, malleable iron is used for pressures up to 350 psi, and steel is used for pressure in excess of 350 psi.

Question of the Month for April 2018

QUESTION:

What are the cold clearances on an average steam turbine?

ANSWER:

Steam turbine clearances are comparatively small.  Radial clearances are 0.180″ to 0.250″, which is the distance between the top moving blades and casing.  Axial clearances are 0.100″ to 0.200″, which is the distance between the nozzle exits and the leading edge of the blade.  Diaphragm gland clearances are 0.002″, which is the distance between the shaft and the bottom of the diaphragm.  Bearing clearances are 0.001″ per inch of diameter of shaft, with a minimum of 0.005″.  A 4″ shaft would rotate in a bearing with an inner diameter of 4.005″, whereas a 10″ shaft would have an inner diameter of 10.010″.

Question of the Month for March 2018

QUESTION:

How should horizontal steam lines be pitched? 

ANSWER:

Horizontal steam lines must always be pitched in the direction of the steam flow and have traps installed at the end of the run so condensate can be removed.  If the lines were piched back toward the boiler, the steam would pick up the condensate and cause water hammer and possible line rupture.

Question of the Month for February 2018r

 

QUESTION:

Can plant efficiency be increased if a closed feedwater heater is used? 

ANSWER:

Yes, it is possible to increase plant efficiency when heating feed water in a closed feed water heater.  A good example of this is when steam is extracted or bled from a high-pressure stage of a steam turbine and used in a closed feed water heater.  The latent heat of the steam is recovered in the feed water instead of being lost in the condenser.

 

Question of the Month for January 2018

QUESTION:

What is the difference between a flush-front and an extended-front horizontal return-tubular boiler?

 ANSWER:

In the extended-front type horizontal return-tubular boiler the front tube sheet is set in line with the front of the boiler setting.  The lower part of the shell extends beyond the tube sheet.  This extension forms part of the smoke box and is known as the dry sheet.

The shell of the flush-front type horizontal return-tubular boiler does not extend beyond the front tube sheet.  The front of the boiler is set back from the front of the setting to allow a space which forms the smoke box.  An arch at the front of the furnace prevents the gases from entering this space and going directly to the stack.