How To Size the Boiler

To Select Boiler.

·         Density of the oil         =900 kg/m³

·         Process settling time     =45-60 min (consider 50 min )

·         final temperature of the oil = 60⁰C

·         specific heat capacity values,

§  oil                    = 2 KJ/kg ⁰k

§  316 SS             =0.5 KJ/ kg ⁰C (Agitator)

§  Mild Steel        =0.62 KJ/ kg ⁰C (kettles)

We have three blending kettles such as 5m³,10m³,15m³.

·         Oil viscosity

§  550-700 (Viscosity @ 40 C mm² /sec (CSt))

§  30-34 (Viscosity @ 100 C mm² /sec (CSt))

·         weight  of kettles

§  5m³  kettle        = 855 kg without manhole weight

§  10m³ kettle      = 1460 kg without manhole weight

§  15m³ kettle      = 2072 kg without manhole weight

·         weight of agitators

§  5m³  kettle        = 51 kg

§  10m³ kettle      = 70 kg

§  15m³ kettle      = 130 kg

Oil processing industry need to select the boiler for their new expansion. Above detail has given by client. There are two demands in steam in process.

1.       Start up                         -              Steam jacketed kettle + Oil heating + Head loss

2.       Continuous operation    -              Oil heating + Heat Losses

Start up

Assumption

1.       temperature increase 30 °C to 60 °C

2.       Operating pressure of boiler considered as 6 bar(g) = 7 bar actual (h_fg@ 7 bar = 2067 kJ/kg)

3.       Heat losses are neglected.

	Calculation	Heat Requirement (kJ)	Steam Requirement (kg)
Steam jacketed kettles	4387 X 0.62 X 30	81,598.2	39.47
Oil heating	30 X 900 X 2 X 30	1,620,000	783.74
Agitators heating	251 X 0.5 X 30	3765	1.82
Total			825.03

Initial steam requirement is 825.03 kg at 6bar(g) operating pressure.

Calculating Steam Rate

They need to heat up the system within 50 min.

Steam flow rate                =             825.03 X (60 /50)

                                        =             990.03 kg/hr

Continuous Operation

In this time steam jacketed kettle has heated to 60 °C. Similar calculation

	Calculation	Heat Requirement (kJ)	Steam Requirement (kg)
Oil heating	30 X 900 X 2 X 30	1,620,000	783.74
Total			783.74

Calculating Steam Rate

They need to heat up the system within 50 min.

Steam flow rate                =             783.74 X (60 /50)

                                        =             940.48 kg/hr

There is no big difference in star up and the continuous operation. So ideal steam requirement is 990kg/hr.

Multiply 10 % factor for losses of the system.

20% additional factor considers. This is due to feed water temperature and operating pressure of the boiler. This reduces the boiler capacity.

Final Estimated Boiler capacity   =             990 X 1.1 X 1.2

                                                 =             1306.8 kg/ hr

1500 kg/hr (F&A 100 °C) Boiler meet the client requirement.

How Do You Identify Actual Boiler Capacity

What is Boiler Capacity ? 

Boiler capacity can express as Steam Evaporation Rate or Energy Transfer Rate of Boiler.

Factors Depends on the Evaporation Rate

1. Operating Pressure.

2. Operating Temperature.

3. Feed water temperature.

4. Dryness fraction. (dryness fraction = mass of steam / mass of Steam & water)

5. Energy Input ratio. (This would be constant because furnace design for specific combustion ratio)

6. Surface area of the water plane of boiler. (this would be constant because it is design factor but level can change due to )

Boiler Capacity Measurements

1. Pounds per hour (PPH)

 pound is a unit of mass.

1 lb = 0.453 592 37 kg

2. British Thermal Unit (BTU)

Boiler capacity express as Energy Transfer rate. Energy measured by BTU. Capacity express as BTU/hr.

W = (hg - hf) x m 

 W - Boiler Capacity(Btu/hr)
hg - Enthalpy Steam (Btu/lb)
hf - Enthalpy Condensate (Btu/lb)
m - Steam Evaporation (lb/hr)  

3. Boiler House Power (BHP)

Amount of Energy required to produce 34.5 lb of steam / hr. Operating Pressure and Temperature respectively 1 bar absolute pressure  and 100^oC and feed water temperature 100^oC at 1 bar (absolute).

1 BHP = 33479 Btu/hr

4. Ton per hr (TPH)

Amount of Steam generate by the boiler per hour at 1 bar(absolute) pressure and 100^oC temperature. Feed water temperature should be 100^oC at 1 bar (absolute).

Evaporation Capacity of Boiler  = 1000 kg /hr (F&A 100^oC)

This means the boiler Evaporation capacity 1000 kg of steam at feed water temperature 100^oC and boiler operating pressure  1 bar(Absolute) or 0 bar(gauge)

 

What Factors to be Consider When Selecting Boiler Capacity

First step is calculate the Average Energy requirement for the Plant. Peak Energy consumption rate also very important when selecting new Boiler for the Plant. Energy consumption rate can shown by kJ/hr or k cal/hr. After define the energy consumption rate; need to know the maximum temperature requirement of the plant. Because operating pressure will change according to the temperature requirement. at 1 bar (absolute) operating pressure and 100^oC feed water temperature boiler out put is optimum. But in higher operating pressure and low feed water temperature cause to reduce the boiler capacity. 

Extra Energy use to

1. Increase the feed water temperature up to 100^oC.

2. Increase water temperature up to boiling temperature which is higher than 100^oC due to high operating pressure. 

Actual Capacity Calculation of Boiler

Defined capacity                 =    A  [1000 kg /hr (F&A 100^oC) ] 

Operating Pressure             =    q  [10 bar(g)]

Feed water temperature      =    T  [80^oC]

 

Actual Boiler Capacity =  A x  hfg @ 1 bar / ( hg @ q bar - hf @ T )

This Equation can use easily to calculate the actual boiler capacity. Specific Enthalpy Should be taken from Steam Table. (Google Down load search - Thermodynamic and Transport Properties of Fluid - SI Units -  G.F.C Rogers and Y.R Mayhew )

Different Between Thermic Heater and Steam Boiler

What is thermic heater ?

thermic heater produce thermal energy by burning fuels(coal/ wood/ saw dust/ paddy husk/ oil).

Thermal energy charge in to thermic oil which is higher boiling point.

Thermal energy transfer through Thermic oil.

Users 

high temperature needs like more than 200 C. 

Eg : Hanwella Rubber Products Limited. 

What is steam boiler?

Generate steam by burning the fuels.

Steam use for heat and pressure requirement. 

Heat needs 

Tea withering, curing, drying, apparel, knitting industries.

Eg : Hayleys MGT knitting Mill, MAS, Brandix, load Star 

Pressure needs 

steam turbine operation.   

Eg : Norochchole Power plant - operate steam turbine, Sugar Industry operate mills by direct steam pressure  

Can use steam boiler for higher temperature needs? 

There is some limitation to use steam boiler for higher temperature needs.

If required temperature 200 C  steam pressure should be 16 bar (16 kg/cm2  or 230 psi) 

more safe use low pressure(4 bar thermal oil ) thermic heater instead of use high pressure (16 bar steam) steam boiler.

 

Relationship Between Temperature and Pressure of Saturated Water and Steam

T = 100 X [ ( P )^0.5 ]^0.5

T - Temperature Celsius

P - Pressure  bar 

This equation can use instead of steam table. 

Steam table available in 

thermodynamic and transport properties of fluids pdf