Unit 12: Elements of Boiler Systems

Question 1

Complete Combustion Products?

Answer 1

Carbon Dioxide, Water, & Sulfur Dioxide

Question 2

What is complete combustion?

Answer 2

Is when enough air, turbulence, temperature, and time is supplied to provide every element enough oxygen to burn completely. Complete combustion allows for the most heat energy to be generated from the fuel being burned.

Question 3

Non-Combustible elements turn into what?

Answer 3

They turn into ash or pass through the furnace unchanged.

Question 4

Products of incomplete combustion?

Answer 4

If the conditions for complete combustion are not present then these elements will be produced in the furnace:

1) Carbon Monoxide
2) Free Hydrogen atoms
3) Free Sulfur atoms

Question 5

What element to look for when testing for incomplete combustion?

Answer 5

Carbon monoxide as it will be the most prevalent of the elements created by incomplete combustion.

Question 6

What is soot made of?

Answer 6

A product of incomplete combustion of carbon elements that did not bind to oxygen. Both carbon monoxide and carbon dioxide are invisible.

Question 7

Most common element in atmosphere?

Answer 7

Nitrogen at 78% and then oxygen at 21% for second place

Question 8

Theoretical Air

Answer 8

The exact amount of air required for complete combustion to take place. Although the theoretical air is never the amount actually used for complete combustion. More oxygen is always required in practice to full expose the fuel elements to the oxygen. The real amount required is called the combustion air and includes the excess air in its calc.

Question 9

Excess Air

Answer 9

The extra supply of air required for complete combustion to practically occur.

Question 10

Combustion Air

Answer 10

The amount of actual air required for complete combustion to occur. It is equal to theoretical air + excess air

Question 11

Percentage of Excess Air Calculation?

Answer 11

Excess air = (Combustion Air - Theoretical Air )/ Theoretical Air

Question 12

Viscosity

Answer 12

Viscosity is the resistance of a fluid (liquid or gas) to a change in shape or movement of neighbouring portions relative to one another. Viscosity denotes opposition to flow

Question 13

Refractory

Answer 13

Materials that can withstand very high temperatures

Question 14

Fuel Oils

Answer 14

Liquid fuels used for boiler firing that derive from petroleum. The petroleum or crude oil is refined through distillation and separated into different hydrocarbons/fuel oils.

Question 15

Fuel Oil Grade Differences?

Answer 15

There are 6 grades/classes of fuel oils and the first 1 class is the one with the least viscosity, lowest heating value, and lowest flash point. 
While the 6th class of fuel oils is the most viscous, provides the largest heating value, and has the highest flash point of all the classes.

Question 16

Ask Clinkers

Answer 16

When fuels are burned they can create soot/ash and this can attach to refractory. Over time it can damage the refractory and peel it off.

Question 17

Biomass

Answer 17

Are solid biofuels such as:

Hog Fuels
Vegetable waste
Wood Waste
Pulp/Carboard
Wood Pellets
Municipal Wastes

Question 18

Solid Fuel Firing Systems

Answer 18

Mechanical Stockers: Feeds solid fuels directly into furnace
Pulverized Fuel Feeder: solids fuels are turned into a fine dust and fed into the furnace through air pipes.
FBC

Question 19

FBC

Answer 19

Fluidized Bed Combustion:

In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.) through which jets of air are blown to provide the oxygen required for combustion or gasification. The resultant fast and intimate mixing of gas and solids promotes rapid heat transfer and chemical reactions within the bed. FBC plants are capable of burning a variety of low-grade solid fuels, including most types of coal, coal waste and woody biomass, at high efficiency and without the necessity for expensive fuel preparation (e.g., pulverising). In addition, for any given thermal duty, FBCs are smaller than the equivalent conventional furnace, so may offer significant advantages over the latter in terms of cost and flexibility.

FBC reduces the amount of sulfur emitted in the form of SOx emissions. Limestone is used to precipitate out sulfate during combustion, which also allows more efficient heat transfer from the boiler to the apparatus used to capture the heat energy (usually water tubes). The heated precipitate coming in direct contact with the tubes (heating by conduction) increases the efficiency. Since this allows coal plants to burn at cooler temperatures, less NOx is also emitted. However, burning at low temperatures also causes increased polycyclic aromatic hydrocarbon emissions. FBC boilers can burn fuels other than coal, and the lower temperatures of combustion (800 °C / 1500 °F) have other added benefits as well.

Question 20

Bubbling FBC

Answer 20

Provides just enough air velocity for the solid fuels and bed materials (Limestone/gravel/sand) to act like a liquid with air bubbles or pockets intermixed. Only small particulates escape from the furnace due to the rate of air velocity. Watertubes are just below the bed materials or in the bed.

Question 21

Circulating FBC

Answer 21

Has a high air velocity rate (around 6-10 m/s) that circulates solids fuels and the bed materials from the furnace and are recaptured and feedback into the furnace. Smaller particulates are still captured by a cyclone separator and removed allowing for complete combustion of larger pieces of fuel. Generally has a higher combustion efficiency then a bubbling FBC because of the increased fuel to oxygen mixing.

Question 22

Benefits of FBC

Answer 22

Fuel Flexibility
Smaller Plant size
Less fuel preparation than most other solid fuel furnaces
High combustion efficiency
Improved regulatory compliance as the temperature is too low for NO2 to form and limestone in the bed acts as a desulfurizing agent.

Question 23

Disadvantages of FBC

Answer 23

Fan power require 3 times the power requirements to reach air velocity
The bed materials need to be replaced
Is not very cost-effective at low operating temperatures or low use.

Question 24

Mercaptan

Answer 24

Is a compound added to natural gas for leak detection purposes as it can be smelled. It smells like rotten eggs.

Question 25

What does a gas burner do?

Answer 25

Mix air and fuel
ignition of fuel
Monitor the combustion process and cut off fuel if flame fails
Control the firing rate in accordance with demand
Shutdown when certain safety limits are pass such as pressure or low water levels

Question 26

Premix Burner

Answer 26

Mixes gas fuels and air before it is ignited/burned. Generally used on small boilers.

Question 27

After Mix Burner

Answer 27

Air is mixed with the gas fuel at the point of ignition or where the burner is located. These can be used on a wide variety of boilers.

Question 28

Types of After-Mix Burners

Answer 28

Multi-spud Burner: has many small burners focused at different sections of the furnace
Ring Burner: used on large boilers. just shoots a large flame in a cyclone

Question 29

Pliot Burners

Answer 29

Lites main burners of gas fire heating equipment

Question 30

Continuous Pilot Burner

Answer 30

It Burns at all times and must be manually ignited. Usually found on small boilers

Question 31

Intermittent Pilot

Answer 31

Automatically turns on at the start of each burner operating sequence, and auto shuts down with the main burners.

Question 32

Interrupted Pilot burner

Answer 32

Auto starts and shuts off once the flame is proven for 10 seconds. This is the safest pilot burn and is used on the largest of boilers

Question 33

SSOV

Answer 33

Safety shut-off valves are used to quickly extinguish burners in case of power loss or other set adverse conditions. They open slowly and close immediately. Normally closed

Question 34

Atomization

Answer 34

Before liquid fuels can be burned properly they must be broken up into a fine spray/vapor. This increases the surface area of the liquid slow allowing it to vaporize much easier. This process is called atomization.

Question 35

Air Atomizing Burners

Answer 35

Uses compressed air to break up liquid fuels into vapors which can be ignited. Generally used for light fuel oils classes 1 & 2 but can be used for heavier fuels if they are heated enough.

Question 36

Steam Atomizing Burner

Answer 36

Steam is used to atomize heavier fuel oils because the steam can heat the liquid fuels up as they come out of the nozzle. Used on larger boilers but operates much the same way as an air atomizing burner.

Question 37

Mechanical Atomizing Burner

Answer 37

Oil is pumped under high pressure through special slots in the burner novel and spun around to properly atomize the liquid fuels. Used on all sizes of boilers. Generally these burners must run at a constant rate and are considered two positions. Although multiple nozzles can be installed in a cluster to vary the fuel supply along with demand.

Question 38

ID fans create a what in the furnace?

Answer 38

They lower the pressure in the furnace

Question 39

Single Element Feedwater Control System

Answer 39

Responds only to the drum or shell level of the boiler. Works well on boilers with steady steam demand applications.

Question 40

Boiler level Swell

Answer 40

when a rapid unexpected use of boiler’s steam, there is a momentary drop in pressure. Which causes the water in the drum to expand which will show a level rise momentarily. This can cause issues in a single element feedwater control. The level controller will not pump the required feedwater into the drum.

Question 41

Boiler Level Shrinkage

Answer 41

When a boiler’s steam demand suddenly stops this can increase the drum’s pressure. Which in turn will cause the water level in the drum to further compress and shrink. In a single element feedwater control, this can cause issues. Especially if this occurs often.

Question 42

Two-Element Feedwater Control

Answer 42

Responds to both the drum level and the steam flow. This will significantly reduce the effects of swelling and shrinkage. Used on larger power boilers only

Question 43

Three-Element Feedwater Control

Answer 43

Responds to the drum level, steam flow, and feedwater flow. This will significantly reduce the effects of swelling and shrinkage. Used on larger power boilers only

Question 44

Why is properly treated make up water so important for boilers? what does it prevent?

Answer 44

Properly treated make up water prevents scale, foaming, and corrosion in boiler waterside piping.

Question 45

Purpose of a Deaerator?

Answer 45

1) Preheats feedwater to lessen thermal shock
2) Stores a reserve of feedwater about 20 mins
3) Removes dissolved gases Oxygen and carbon dioxide from the feedwater

Deaeration protects the steam system from the effects of corrosive gases. It accomplishes this by reducing the concentration of dissolved oxygen and carbon dioxide to a level where corrosion is minimized.

Question 46

Bottom Blowoff Valves Order of operation?

Answer 46

The closest valve is a quick opening valve and will be open first to act as a guard valve
The slow-opening valve is opened last to blowoff the boiler for dissolved solids and gasses

Do this in reverse to stop blowdown