3. Steam, electricity, and compressed air

Question 1

What is a boiler

Answer 1

vessel that heats water to become hot water ot steam a closed container with water under pressure in it. it’s housed in a building that is frequently separated from the main processing area

Question 2

Fuel of boiler?

Answer 2

1. Fuel oil (solar/diesel oil, MFO)
2. Gas fuel (natural gas)
3. Solid fuel (coal, solid waste, biomass)
4. electricity (heating element) –> lab boiler

Question 3

Primary req of boiler

Answer 3

1. water must be contained safely
2. Steam must be safely delivered in desired condition (as regard its pressure, temperature, quality and required rate)

Question 4

Types of boiler and their explanation

Answer 4

1. Fire tube boiler:
   a) hot combustion gases run through the boiler tubes
   b) relatively small steam capacities (12,000kg/h)
   c) low to medium steam pressures
   d) operates with oil, gas, or solid fuels

2, Water tube boiler
a) used for high steam demand and pressure requirements
b) capacity range of 4,500-120,000 kg.h
c) lower tolerance for water quality and needs water treatment plant

Question 5

Boiler fittings and accessories

Answer 5

1. Pressure gauge: attached to the boiler where it will be directly connected to the steam space
2. Steam pressure regulating valve: steam in boiler will be at a higher pressure than the steam required in the system, necessary to have a valve in place between boiler and the system to reduce pressure of the steam to the required pressure in steam transfer system, whenever a reduction of pressure must occur, a pressure-regulating valve is required
3. safety valve: designed to open when the set pressure is exceeded. it will remain open and blow until the pressure is reduced to 14-28 kPa below the pop-off pressure
4. Steam trap: steam will condense somwehere in the pipe work and become contaminated with moisture. steam traps are devices that will remove water from steam line. most widely used mechanisms are those that rely on differences in temp, specific gravities, and pressure. types: float, inverted bucket, ball float steam
5. water columns: used to check water level inside the boiler
6. water injection: injected into boiler by means of a high-pressure makeup pump.

Accessories fitted: responsible to increase the efficiency of the boiler such as: super heater, economizers, feed pump, air pre heater, steam injector

Question 6

Causes of poor boiler performance?

Answer 6

• poor combustion
• heat transfer surface fouling
• poor operation and maintenance
• deteriorating fuel and water equality

Question 7

Avoidable losses which can be reduced such as

Answer 7

• stack gas losses (excess air, stack gas temp)
• losses by unburnt fuel
• blow down losses
• condensate losses
• convection and radiation

Question 8

Boiler efficiency can be calculated through thermal efficiency by 2 methods:

Answer 8

1) direct method: energy gain of the working fluid (water and steam) is compared with the energy content of boiler fuel
2) indirect method: difference between losses and energy input

Question 9

boiler efficiency: direct method

Answer 9

(n) = (heat output/heat input) x 100
= {[Q x (hg - hf) ] / (q x GCV)} x 100

Question 10

heat loss method (indirect method) calculation

Answer 10

ultimate analysis of fuel…. cek slides ajh

Question 11

Boiler blow down functions:

Answer 11

1. controls TDS (total dissolved solids) in water that is boiled
2. blows off water and replaces it with feed water (make up water)
3. conductivity measured as indication of TDS level

Question 12

calculation of quantity blow down required:

Answer 12

Blow down (%) = (feed water TDS x % Make up water)/ (max. permissible TDS in boiler water)

Question 13

2 types of blow down

Answer 13

1. Intermittent
   - Manually operated valve reduces TDS
   - large short-term increases in feed water
   - substantial heat loss
2. Continuous
   - ensures constant TDS and steam purity
   - heat lost can be recovered
   - common in high-pressure boilers

Question 14

benefits of boiler blow down

Answer 14

• lower pretreatment costs
• less make up water consumption
• reduced maintenance downtime
• increased boiler life
• lower consumption of treatment chemicals

Question 15

Alternating current (AC) vs. direct current

Answer 15

AC:
1. direction of current changing several times/sec
2. unit of frequency is Hertz, meaning cycles/sec

DC:
1. Voltage changes over time but polarity (direction of current flow) stays the same
2. direction of electron flow/current stays the same

Question 16

Single phase vs three-phase power

Answer 16

Both refer to units using AC power. However, primary difference is constancy of delivery.

Single phase:
- Peaks in voltage 90 and 260 degree, with a complete cycle at 260 degree. With these peaks and dips in voltage, power is not delivered at a constant rate
- one neutral wire and one power wire with current flowing between them
- cyclical changes in magnitude and direction usually change flow in current and voltage about 60 times/sec

three-phase:
- there are 3 power wires, each 120 degree out of phase with each other
- by the time a complete cycle of 360 is completed, three phases of power have each peaked in voltage twice
- power stream is delivered at a constant rate, making it possible to carry more load

Question 17

Basic electrical system requirements:

Answer 17

1. Power source
2. Load device
3. conductors “accessory components”
4. switch
5. fuse

Question 18

Important metrics:

Answer 18

Ampere:
1A = 1 C/s

Volt:
1V = 1J/C

Resistance:
R= V/I = ohm and V= IR

Watt:
W= V x A = (V x I) joule/sec

W = (I^2 x R) J/s

W= (I^2 x R x t) J

1 kWh = 1000 J/s (3600 sec) = 3.6 x 10^6 joul

Question 19

cycles refer to the refers of the current in AC circuits. current is reversed 60 cycles or 120 times/sec. when a 60-cycle motor is connected to a 50-cycle circuit, it will only run 5/6 its rated speed

Question 20

Characteristics of a series circuits:

Answer 20

1. The current is constant throughout the circuit
2. The current (A) must pass through each component in the circuit
3. The total resistance of the circuit controls the current in the circuit
4. The total resistance of the circuit is the sum of all the resistance’s in the circuit
5. The sum of the voltage drops across the resistors will be equal to the applied voltage

Rtot= R1 + R2 + R3 + Rn

Question 21

characteristics of parallel circuit:

Answer 21

has two or more loads connected so that current can divide and flow through the load.
1. Current has many paths
2. Resistance in each load will determine the current flow for that resistance
3. Total resistance will always be less than the smallest resistance in the circuit
4. The voltage drop across all loads will be battery voltage

Rtot= (R1 x R2)/ (R1+R2)

1/Rtot = 1/R1 + 1/R2 … + 1/Rn

Question 22

Ohm’s law

Answer 22

V = I x R

Question 23

Symbols in electrical schematics cek di slides wak

Question 24

DVOM is used for? features?

Answer 24

To check inputs on machines equipped with an electronic control module (ECM) or electronic control unit (ECU). Features: voltage testing, amperage testing, and resistance testing

Question 25

Compressed air acts as..

Answer 25

an energy source for a variety of tools and machinery, so it is often integrated part of many production process

Question 26

Compressor is often used for?

Answer 26

1. Generating movements and lifting, or to clean, move or cool materials
2. Increasing pressure of air from low to high pressure by using some external energy

• movement of material (powdered product, grain)
• operation of controls
• drying system (atomization in spray dryer)

Question 27

Compressor types

Answer 27

Intermittent flow (positive displacement)
a) reciprocating -> mechanical piston
b) rotary -> sliding vane, liquid piston, helical lobe, straight lobe

continuous flow (dynamic and ejector)
dynamic:
a) radial flow -> centrifugal
b) mixed flow -> mixed flow
c) axial flow -> axial

Question 28

Positive displacement operates by..

Answer 28

trapping a specific volume of air and forcing it into a smaller volume

Question 29

centrifugal operates by accelerating

Answer 29

the air and converting energy to pressure

Question 30

what’s the principle and components of reciprocating compressor?

Answer 30

Principles
low mass flow rate, service life longer, high pressure ratios, bigger size, relatively cheap

Primary components:
1. compression cylinders, stages of which a particular design may have from one to six or more, provide confinement for the process gas during compression
2. piston is driven in a reciprocating action to compress the gas

Question 31

Drive motor:

Answer 31

a) combustion
b) electric

Question 32

refer to slide reciprocating compressor (double stages), components and acc

Question 33

In a reciprocating compressor, a volume of air is….

Answer 33

drawn into a cylinder, it is trapped, and compressed by piston and then discharged into the discharge line

Question 34

Rotary-screw compressor principles

Answer 34

• quiet operation
• high volume of air, steady flow
• lower energy cost, small size
• suitable for continuous operation
• low efficiency
• low pressure ratio

Question 35

Principles of centrifugal compressor

Answer 35

accelerates the velocity of the gases (increases kinetic energy) which is then converted into pressure as the air flow leaves the volute and enters the discharge pipe. it delivers much higher flow rates than positive displacement compressors

Question 36

Basic components of centrifugal compressor

Answer 36

1. impellers, vanes, volutes, suction eyes, discharge lines, diffuser plates, seals, shaft, casing
2. suction vane tips = part of the impeller vane that comes into contact with air first
3. discharge vane tips = part of the impeller vane that comes into contact with air last

Question 37

Axial flow compressor principles

Answer 37

1. composed of a rotor that has rows of fan like blades
2. air flow is moved along the shaft
3. rotating blades attached to a shaft push air over stationary blades called stators
4. stator blades are attached to the casing
5. as the air velocity is increased by the rotating blades, stator blades slow it down. as air slows, kinetic energy is converted into pressure
6. air velocity increases as it moves from stage to stage until it reaches the discharge
7. multi-stage axial compressors can generate very high flow rates and discharge pressures

Question 38

Trivia:

Definitions of Compressor
* Compression ratio:- It is defined as the ratio of volume of air before compression to the volume of air after compression.
* Compressor capacity:- It is the quantity of air actually delivered by a compressor in m3/minute or m3/sec.
* Free air Delivered (FAD):- It is the volume of air delivered by compressor under the compressor intake conditions ( i.e.
temperature and pressure ).
* Swept Volume:- The volume displaced or swept by piston when it moves between top dead center and bottom dead center.
* Clearance volume:- it is the difference between the total volume and the swept volume, basically the gap that remains between the piston head and the cylinder head when at top dead center.

Question 39

Trivia

Answer 39

Definitions of Compressor
Efficiencies:
* Volumetric efficiency:- It is the ratio of actual volume of the FAD at standard atmospheric condition in one delivery stroke (Actual air intake) to the swept volume (theoretical air intake) by the piston during the stroke.
* Isothermal efficiency:- It is defined as the ratio of isothermal power (Piso) (i.e. required input power at isothermal process) done to the indicated power (IP) or actual work done.
* Mechanical efficiency:- It is the ratio of indicated power (IP) to the shaft(Brake) Power (Pshaft).
* Overall efficiency:- It is the ratio of isothermal power (Piso) to the shaft(Brake) Power (Pshaft).