PT 2 Boiler Combustion and Firing Methods Test 1

High Gas Pressure Switch

Contacts normally closed whenever the main gas line pressure is above a present pressure. Should the pressure rise, switch contacts open, causing the main gas valve to close. It ensures stable combustion and correct air-fuel ratio during operation of the boiler. Manual reset on this switch and is located AFTER the low gas pressure cutoff.

What is theoretical Air?

Theoretical air is the amount of air needed for combustion. In practice, this is not enough so we feed the furnace with excess air

Insufficient boiler room air supplied results in?

-sooting on heat transfer surfaces -plugging of flue gas passes -poor heat transfer -increased fuel consumption -danger of explosions due to fuel rich furnace -CO poisoning

4 Methods to measure fuel oil level in the tank

1)Using a dip stick with the measuring well 2)using a retractable measuring weight used to find level 3)Pneumercator ("level indicator") 4)Using Bullzeye Sight Glass (rarely see now due to environmental concerns and leakages)

Summarize the process of going from lump coal to a steam generating unit.

1. Coal is reclaimed (transfer of bulk coal to bunker) and crushed to the proper size in the crusher house (1-2" diameter). 2. Coal is then fed to the surge bin where magnets remove any impurity metals. 3. From the surge bins, coal is taken by conveyer belt to the plant silos (or bunkers). 4. Each bunker has a coal feeder which feeds in a pulverizer. Pulverized coal now in the form of coal dust, is piped into the steam generator for combustion.

Major lost during incomplete combustion and why is this a concern?

A percentage of available heat is lost during incomplete combustion. Since fuel is generally the highest cost of a plant, burning it efficiently is crucial for successful operation.

Describes how the atomizing air compressor works

A small compressor supplies atomizing air to atomize the oil. Oil travels down central tube while the primary air moves down the other tube. Air blows the oil through n atomizer into a fine spray and swirls the oil mist into the furnace. The fuel enters the atomizing stream at or near 90 degrees thus creating a shearing action on the fuel as it enters the atomizing steam. Combustion air (secondary air) is blown into furnace by the FD fan. Combustion air swirls in the opposite direction to the oil mist, resulting in good, turbulent mixing.

What is the sump in the tank farm used for?

A sump is a low collection point in the farm to collect water, melted snow, etc. We can also use it to sample for oil presence (oil leaks)

Another method to lower thermal NOx emissions?

A third method is to adjust the fuel feed position, thus changing the flame pattern. NOx natural gas burners have a longer, more orange flame.

What other concerns do we have when burning a certain fuel?

Also concerned with the environment and sometimes cost of fuel prohibits plant operations.

What is excess air?

Amount of air supplied above theoretical air

Flue Gas analysis

Analysis of flue gas emissions allow us to determine the success of combustion. We measure Carbon Dioxide, water, Sulphur Dioxide, oxygen and Nitrogen. Bu analyzing the flue gas, we can determine the completeness of combustion as well as the effectiveness of any flue gas handling equipment.

Fixed Fuel Oil Storage

Capacity should be sufficient for 1 week (for urban setting). For rural or distance setting, storage should be maintained for about 3 weeks.

Main Gas Valves

Are ON/OFF, normally closed, single-seated gas valves.These valves operate automatically as directed by the boiler programming control. They open when the valves are energized.

Air Atomizing Oil Burner on Packaged Units

Atomizing air compressor on side of packaged boilers. These units do not rely on external source of compressed air. Delivers primary air for combustion.

ASR Burner

Axial, Staged, Return Air Burner uses air staging. This involves the combustion air being fed in several stages, separating the primary and secondary air to slow combustion.

Describe the Barrel Crusher

Before we store coal into silos, we need to crush it down to size. We use rotating sets of hammers. As the coal enters the top it gets crushed to 25-50cm and drops into the hopper, where it is delivered by a separate conveyer belt to the silos.

Describe turndown in multiburner systems

Burner turndown refers to how much you can lower the fuel pressure to control the firing rate before the limit of stability (range that a gun allows for a stable flame) is reached. When the turn down pressure reaches this point, any further reductions in the firing rate requires that one or more burners need to be shut down to maintain stable fuel pressure and fire.

Describe Coal Handling

Coal handling is highly mechanized and even remotely controlled. Together with the ash removal system, it accounts for a large part of the investments cost and is often the major maintenance item.

What does proper/improper combustion lead to?

Combustion is the burning of fuel to produce heat. Improper combustion leads to boiler fouling, unwanted emissions, and increased cost of operation. Proper combustion ensures the safety of the operator and plant staff.

What is combustion?

Combustion is the rapid oxidization of fuel which produces large quantities of heat.

Main Gas Pressure Regulator

Controls the main gas pressure at a higher setting then the pilot regulator. This produces a steady flame and helps obtain the highest combustion efficiency.

Above Ground Storage Tanks for Fuel Oil

Cost less and creates fewer pumping problems, plus all equipment is accessible for maintenance, but takes up more real estate. They also require a dyke surrounding the farm large enough to contain all of the volume of the fuel + 1/3 extra.

DAF burner

Distrubuted Air Flow burner uses isokinetic spinner to create a recirculation zone. By recirculating the flue gas back into the burner front, it ensures that all combustible elements in the fuel are burned and reduces amount of excess oxygen required for complete combustion. Primary air gets in contact with gas first and mixes, then it mixes with secondary air in the opposite direction to cause recirculation.

Externally mixing burner

Easier to clean less likely to clog -2 tubes-centre carries oil to tip -steam through outer tube -mixed at the nozzle tip

In which part of the furnace will complete combustion be achieved?

End of the radiant zone, the furnace exit.

Fill line and Vent Pipe on Fuel Oil tank

Fill line is lower then suction line. Vent piping is venting the tank

What type of atomization does our boilers use in the power lab?

Fire tube boiler uses air atomizing gun Watertube boiler uses mechanical atomization

What is the steam smothering line/Fire Connection used for?

Foam or steam is used to extinguish fire in tank to flush our oxygen in it.

Administrative Fuel Oil Storage

Fuel is gaurenteed by contract. While it is not as reliable as having fuel storage on site, it is a contractual obligation from the supplier which have financial repercaussions if not met.

What are fuels composed of? and what do they form?

Fuels are composed of both combustible and non-combustible elements. They form hydrocarbons when they are chemically combined.

Ring Type Burner

Gas is supplied to a ring type manifold, which has numerous gas outlets drilled in it. Air is admitted through air register louvers and passes through the centre of the ring. There it mixes with the gas issuing from the holes in the ring manifold.

What three types of fuels do we use in NB?

Gas, Oil, and Coal

Combustible Elements

Hydrogen, Sulphur, Carbon

What happens if air supplied to boiler is low?

If air supplied for complete combustion is low, it produces free carbons which presents itself as black smoke from a stack which is visible by the eye.

What occurs if excess air is too high? Too low?

If excess air is too high we get heat losses up the stack. Also have to deal with NOx emissions if it is too high. If it is too low we increase the possibility of incomplete combustion.

What is ACTIVE storage?

In active storage, the coal is directly fed into the silos by a drag scrapper which drags (uses pullys and bucket system) to dump the coal in the silos

What is a RESERVED storage pile?

In the reserved storage pile, the coal is stored for a extended period of time. It gets packed down to eliminate risk of moisture or air entering our pile. These will reduce the heat capability of the coal over time due to the oxidization of the coal.

Advantages and Disadvantages of the Rotary Cup Oil Burner

It does not rely on fuel pressure and only used for light fuel oil. It relies on two fans, the FD fan and the primary air fan. This in turn means there are many mechanical rotating parts, but it does not clog up as easy.

Suction Line on the fuel oil tank

It is tied into the pump. One suction line at the bottom of the tank and other is higher incase water or sludge is settled on the bottom of the tank.

What does an unstable ignitor mean?

It might not lite the main gas line and push fuel that is unburned through the boiler

2 types of above ground storage tanks for fuel oil

Large Cone Roof Tank and Floating Roof Tank (roof floats on top of oil to prevent air from entering)

What is Coal Silo-arching?

Moisture in the coal that causes us problems because we cannot directly feed boiler from the bunker because it gets too tightly packed and stuck. Also known as "rat-holing" which reduces the capacity of the silo

Non-Combustible elements

Moisture, Ash, Carbon Dioxide

Online-analyzer

Monitors flue gas emissions in the stack continuously.

Concern with boiler room air

Must have sufficient openings and supply equipment to deliver enough capacity for combustion air, as well enough to make the environment habitable.

Fuel Types

NO6-Bunker C -residual waste of oil - Heavy Fuel Oil (HFO) NO2-Fuel Oil -Light Fuel Oil

Why are NOx emissions bad?

NOx emissions (Nitrous Oxide and Nitrogen Dioxide) contribute to smog pollution through a chemical reaction with the sunlight. In the presence of other hydrocarbons, NOx emissions can form cyanides.

Typical amount of excess air for natural gas? Coal?

Natural gas = 3-15% Coal = 25-40%

Natural Gas and its relationship to Combustion air

Natural gas is already in a gaseous state (vapour) so there is no need for further atomization in the burner. The burner must be able to control the amount of air admitted to burn the gas and must be able to cause turbulent mixing of the gas and air. Most burners have the fuel entering the combustion air stream at (or close to) right angles, which promotes good mixing.

Describe Thermal NOx

Nitrogen and oxygen in combustion air react at high temperatures to form NOx. Occurs rapidly above 1535 degrees Celsius. This is the greatest source of NOx and receives the greatest attention in controlling NOx emissions.

Describe Prompt NOx

Nitrogen component of the combustion air reacts with hydrocarbon combustion products. Very minor source of NOx compared to total NOx production.

Describe Fuel NOx

Nitrogen compound of the fuel reacts with oxygen in the combustion air to form NOx. Since natural gas normally has a low nitrogen content, fuel NOx is not a concern.

Internal mixing type (emulsion atomizer)

Oil and steam admitted to a mixing chamber and the mixture passes through the emulsion tube to the nozzle at the end where it emerges as an atomized spray into the furnace. Internal mixing has better flame control.

Describe the Rotary Cup Oil Burner

Oil is delivered to a cup that is rotating about 3500RPM. Centrifugal force throws the oil from the lip of the cup in the form of a conical sheet of liquid, which quickly breaks into a spray. Primary air is supplied through an annular space around the cup and mixes with the oil leaving the cup, which in turns mix with secondary air.

How does the emulsion atomizer work?

Oil is pumped through an orifice and then blasted by a jet of high-pressure air or steam. Contact between the oil and steam may occur inside or outside the burner tip depending upon the design.

Steam or Air Atomizing Burners (emulsion atomizer)

Operate by producing a steam-fuel (or air-fuel) mixture that atomizes the oil through the rapid expansion of the steam when released into the furnaces.

Whats the difference between permenant storage and a live pile?

Permenant storage is used to store coal for months on end while a live pile is where we actively take from for fuel.

Low Gas Pressure Cutoff Switch

Prevents the burner from operating when the gas pressure in the supply line drops below the pressure necessary to maintain a stable flame at the burner. Should the pressure drop, contacts will open the circuit causing the main gas valve to close. Normally opened valve with a manual reset.

Primary concern with incomplete combustion is? Why is it a concern?

Primary concern is formation of Carbon monoxide with incomplete combustion. CO presents a hazard to the environment and represents a waste of fuel. CO is colourless and is detected by the flue gas analyzer.

Gas Pilot Pressure Regulator

Reduces the incoming header gas pressure. To ensure a satisfactory pilot flame, this regulator maintains a steady and constant pressure in the pilot gas line.

Return line and Sludge Pump for Fuel Oil Tanks

Return line should extend below the level of suction inlet. The sludge pump can be used to suck sediment or water from bottom of the tank.

Solenoid Operated Valve

Solenoid means "coil" Fail safe valve -only opens when it is energized -works on magnitizing by induced voltage -quick open, quick close valve

Hydromotor Gas Valve operation

Spring pressure quickly closes gas valve when solenoid valve denergizes. Solenoid valve keeps fluid in place, so it keeps valve opened when its energized. Opens very slowly (13 seconds) to slowly introduce fuel to furnace so we don't get a furnace puff. It is a open or close valve only (1 second to close)

Multi-Spud Burner (the Coen Burner)

Spuds increase surface area and allows it to spray out properly to mix with air. They are removable for maintenance.

Below Ground Storage Tanks for Fuel Oil

Take up less space and protected from environmental hazards . They are also vacuum insulated (tanks have 2 walls with interstitial tank pressure between them). This will show atmosphere pressure on the pressure gauge if we have a leak inside the tank.

CGA code states what?

The Compressed Gas Association states strict guidelines for providing sufficient air when burning natural gas.

What is the best method for reserved coal storage piling?

The best method is to pack coal tightly and mix coal fines with the rough coal to fill any possible spaces in the pile.

What is used to carry the coal in a coal plant?

The coal is carried by track hoppers from trains, boats or truck loads of lump coal.

When using an emulsion atomizer what must be done with the steam/air?

The steam or air must be dry to avoid pulsations -cannot keep a stable flame, flame scanner trips the boiler.

Handling of fuel oil involves what?

The handling of fuel oil involves storing, heating, pumping and burning the oil. Handling of lighter oils involves the same operations with the except of heating.

Describe the heating of Heavy Fuel Oil

The heating of heavy fuel oil is heated in two stages. The first stage heats the oil in the tank to facilitate pumping. Steam heater is used to heat the oil to 55C to lower the viscosity of the oil. The steam is then returned to sewer to avoid contamination of oil into the condensate return system. The second stage heats the oil to a temperature that will promote atomization in the burners.

What does the idler gear on the conveyer belt do?

The idler gear (or take-up pully) and counter weight is used to take up the tension of belt when weight is added.

Principle functions of an oil burner?

The principle functions of an oil burner are to change the liquid oil into a fine mist, or vapour like state, and to throughly mix this atomized oil with air so that combustion can take place quickly and efficiently.

What is the purpose of the coal plant?

The purpose is to receive the incoming coal supply, place it on stock, then transport it from stock to boilers when required in the proper form.

What is the scavenging line used for?

There for personal protection. Purges the empty tank with nitrogen first then oxygen to remove harmful vapours before an operator enters the tank.

Hydromotor Gas Valve requirements

These gas valves are large due to volume of gas per kg. Requirements: 1) a lot of power needed to move large valve 2)must operate FAST in an emergency Fast operations Safe,simple, and powerful Fail Safe

Mechanical Atomizing Burners

They have a quick detachable coupling which is used to unscrew yoke and retract the gun from the boiler. It uses high pressure oil pump (250psi) to force it through the tip of the gun. ATOMIZES UNDER PRESSURE

What have pollution concerns and high fuel prices make it necessary to do?

They made it necessary to make burners more efficient, using less oxygen and producing less NOx. To use less oxygen, very thorough mixing of air and fuel is required.

What design does mechanical atomizing burners use to atomize the fuel oil?

This design uses the fact that when oil is forced under pressure through a small orifice into an area of lower pressure it tends to break into a spray of fine droplets. You can use this design for any grade of fuel oil.

What 4 things does complete combustion depend on and explain them?

Time, Temperature, Turbulence, and air. To achieve complete combustion of a fuel, the combustible elements must mix (turbulence) throughly with enough oxygen (air) and be given sufficient time (time) to burn, while still exposed to the high temperature (temperature) of the furnace.

How does one achieve lower thermal NOx emissions?

To achieve lower thermal NOx, the flame temperature must be kept as low as possible. This is achieved by using some form of flue gas recirculation, which involves mixing partly burner flue gas with the main flame, resulting in slower burning and cooler flames.

Why are NOx emissions a major challenge to control?

To control them, the temperature of the furnace must be lowered, or the oxides removed from the flue gas. Higher furnace temperatures = more NOx emissions but furnace temperature is one of our 4 needs for proper combustion.

What is tramp metal?

Tramp metal is metals or pieces of wires in the coal that is picked up by a magnet because we do not want these impurities going into our boilers.

Gas Butterfly Valve

Under the control of the damper motor, regulates the rate of gas flow to the burner at all loads. Mechanical linkage is connected to the same motor that opens and closes the air dampers, controlling the amount of combustion air and gas to the boiler.

What does it typically mean when you have poor combustion occurring?

Usually means one of your three T's or air are not being met.

Pressure Regulating Valves for natural gas lines?

Vented directly to the roof so its not vented into the boiler room

Why do we transport coal in a bigger form?

We carry it in a larger form to avoid potential explosion and make it easier to transport.

What else must we monitor in our reserved coal piles?

We must also monitor temperatures to avoid risk of spontaneous combustion

Decribe the operation of the Pneumercater

We use a manual plunger to bubble out oil in the piping to the vented tank.The tube is now filled with air. The height in the oil tank pushes down on the air which flexes bellows and this gets transmitted to a pointer indicating the level in the tank.

Why do we use belt conveyers and what are they made of?

We use belt conveyers as they are they best at handling large quantities of coal required in the power plants. Belts are made of a rubber and canvas composition, which has good tensile strength and is resistant to abrasion and corrosion. They have a curve to them.

What about start up conditions for the emulsion atomizer?

We use compressed air (primary air) to atomize it on start up. Once steam is generated we can switch to steam which produces better combustion.

What do non-combustible elements in the fuel form?

Will either form ash, or pass through the furnace unchanged.

Isokinetic Spinner

known as spinner, diffuser, Rosette, swirl plate or spin plate. Its the plates at the end of the burner which cause air to spin (rotational motion) allowing fuel and air to mix at opposite directions. The spinner is stationary and has angled louvers to promote mixing. Secondary air goes over the louvers.