Basic Questions & Answers on Slop/Spent wash fired Boilers



1-What do you mean by Slop or Spent wash?
Slop or Spent wash also known as Vinasse is an acidic effluent produced in Distillery unit. Slop is formed on fermentation of Sugar cane molasses in distillery.
2-Why do you treat Slop as a Hazardous effluent?
Because it is an acidic effluent having pH around 4 to 5
3-What are the standard parameters of Slop or Spent wash?
  • Colour : Brown
  • Odour : Pungent
  • pH : 4 to 5
  • Solids: 9 to 12%
  • BOD : 45000 to 60000
  • COD : 110000 to 1350000
4-What are the various methods of Slop disposal?
  • Disposal methods:
  • Biomethanation
  • Composting
  • Incineration Technology

5-What is the purpose of using incineration technology for Slop disposal?
Incineration technology method leads to Zero Liquid Discharge, where spent wash is concentrated by heating it in specially designed Boilers.
6-What are the benefits of burning Slop in Boilers?

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Slop fired Boiler start up procedure
Benefits:
  • Zero liquid discharge (ZLD) or Zero effluent discharge (ZED)
  • Steam generated in Boilers can be used for Distillery process
  • Power generation to fulfil auxiliary power of distillery, hence reduction in production cost.
  • Ash generated is of potash reach which is good manure


7-What are the challenging situations for designing the Spent wash Boilers?
  • Slop & its ash characteristics
  • Design of combustion system for Slop
  • Design of combustion system for supporting fuel
  • Design of pollution control equipments
8-Why it is being challenging task to burn the spent wash?
Because it is a liquid fuel having very low GCV up to 1800 kcal/kg & high ash & moisture content.
9-What are the various supporting fuels used in Incineration Boilers?
  • Spent wash + Coal (Indian/Imported)
  • Spent wash + Rice husk
  • Spent wash + Bagasse
10-What type of Boilers are used in Incineration Technologies?
  • Travelling grate Boiler: Rice husk & Bagasse
  • AFBC Boiler: Indian & Imported coal
11-What are the features of AFBC boilers used in Incineration Technology?
AFBC Boiler:
  • Bottom supported
  • Single drum
  • Over bed feeding
  • 3-pass flue gas construction
  • Combustor is located in pass-1 & Super heater, Evaporator; Economiser & Super heaters are located in Pass-3

12-Briefly explain the combustor & fuel feeding system in AFBC boilers?
Combustor:As discussed above, Combustor is located in Pass -1, fabricated with high temperature refractory material, enclosed by steel casing and supporting structure. Combustor is divided into various compartments & for all compartments ash drain system is provided.
Coal feeding system: consists of coal bunker, VFD screw feeders to feed the coal. Coal is distributed inside the combustor by pneumatic spreading system.
Spent wash feeding system: Concentrated and pre-heated Spent wash from the storage tank is conveyed to boiler through variable speed pump. Spent wash is sprayed over the fluidising bed at first pass through spray guns.

13-Where do the Secondary air & spent wash nozzles are provided in AFBC Boilers?
Secondary air system is provided at 2 to 3 locations at various heights at furnace. And spent wash nozzles provided just below the secondary air nozzles
14-What are the various online cleaning mechanisms are provided for pressure parts?
Mechanical rapping systems for super heaters
Soot blowers for Evaporators
Sonic soot blowers for Economisers
15-How do the spent wash concentration (Brix) & its calorific values are related?
GCV of the spent wash increases with increase in its concentrations
Sl No.
Brix (%)
GCV (Kcal/kg)
1
40
850
2
45
1200
3
50
1400
4
60
1800

16-How do you increase the Brix of Spent wash?
Spent wash Brix can be increased by heating
17-What parameters of Brix are recommended for efficient burning?
  • Brix: 55 to 60%
  • Moisture: 40 to 50%
  • Ash: 18 to 20%
  • GCV: 1550 to 1750 kcal/kg


18-Write down the ultimate analysis parameters of Spent wash
  • Ultimate analysis report:
  • Carbon: 18.5 to 23%
  • Hydrogen: 1.5 to 2.5%
  • Oxygen: 12 to 15%
  • Nitrogen: 1.5 to 2%
  • Sulphur: 0.5 to 0.7%
19-What are the various contents of spent wash?
Ash contents analysis by weight is as follow
  • Silica (SiO2) : 2.3 to 2.8%
  • Iron Oxide (Fe2O3) : 2 to 2.5%
  • Calcium Oxide (Cao) : 12 to 16%
  • Magnesium oxide (MgO) : 6 to 7%
  • Sulphate, SO3: 15 to 17%
  • Phosphate (P2O5) : 8 to 12%
  • Potassium Oxide (K2O) : 45 to 50%
  • Chlorides: 0.8 to 1.2%

20-What is the quantity of steam generated per square meter of heating surface in Spent wash AFBC boilers?
It is around 8 to 10 kg of steam is generated per square meter of heating surface
21-What is the quantity of steam generated per square meter of heating surface in Spent wash Biomass (Bagasse, rice husk etc) fired boilers?
It is around 10 to 12 kg of steam is generated per square meter of heating surface.
Note: For incineration:AFBC Boilers have more heating surface as compared to Biomass fired Boilers
22-Why do the Spent wash Boilers have taller furnaces?
Because;
  • To maintain higher residence time in furnace up to 8 seconds
  • To maintain optimum flue gas temperature at super heaters inlet to avoid coils fouling due to alkali ash property and to avoid corrosion of super heater coils due to chlorides (1%) in ash
23-What is the design configuration of APH in spent wash fired Boilers?
In spent wash Boilers APH are designed for air flow through tubes & flue gas outside to avoid choking of tubes
24-What is the flue gas temperature that we get at APH outlet for spent wash fired Boilers?
It is around 180 to 200 Deg C
25-What is the size & density of refractory materials used in Spent wash AFBC Boilers?
Size of refractory materials is around 0.8 to 2.5mm. And density is around 1000 to 1100 kg/m3
26-What are the main compositions of Refractory materials?

Questions & Answers on AFBC Boilers
  • Silica 55 to 60%
  • Alumina 35 to 40% & small traces of Feo, Mno, Cao, Mgo, P2O5 etc
27-What is the optimum temperature of spent wash at the nozzle inlet?
It is around 70 to 80 deg c
28-What is the maximum efficiency that we can get for spent wash & Rice husk fired Boilers?
It is around 72%

Also read:Troubleshooting in Boilers



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How do you calculate the Power generation in steam Turbines??


Power in the steam Turbines produces at every stage where the steam is taken out, whether it may be bleed, extraction or exhaust steam. As the steam out from the turbine increases the power developed on that particular stage will increase.
Power generation phenomenon.
Power generation in steam Turbines is calculated based on difference between the heat content of inlet steam & extracted steam.

Factors affecting the power generation:
  • Power generation at particular stage increases, when there is more steam flow &vice versa
  • Power generation at particular stage increases when there is more difference between inlet & extraction steam & Vice versa
  • Power develop at particular stage decreases if its extraction pressure increases & vice versa
  • Power developed at particular stage decreases if its extraction temperature increases & vice versa
  • Power developed in steam Turbine decreases if inlet live steam pressure & temperature decrease
  • If steam vacuum decreases power generation reduces or else Turbine will consume more steam to develop same power
  • If exhaust steam temperature increases then the power power generation reduces or else Turbine will consume more steam to develop same power
  • If wheel chamber pressure increases, then the power generation capacity of the Turbine decreases
HOW DO YOU CALCULATE POWER GENERATION COST??

In which part of the Turbine higher power can be produced at lower steam consumption? And why?
It is at the exhaust stage. Because at the exhaust stage pressure & temperature of the steam is very lesser than bleed &extraction stages.
In which part of the Turbine lowest power is produced at higher steam consumption? And why?
It is at the bleed stage. Because at bleed steam pressure & temperatures are higher than extraction & exhaust stages
Calculation part:
1-Calculate the power generated in a back pressure steam Turbine, where 50 TPH steam enters the Turbine at 66 kg/cm2 & temperature 485 Deg C.And steam exhausts to process at pressure 2 kg/cm2 & temperature 180 Deg C.
For calculation of power we need to know the enthalpy of inlet & exhaust steam.
Refer steam table
Enthalpy of inlet steam at rated parameters H1 = 806.5 kcal/kg
Enthalpy of inlet steam at rated parameters H2 = 677 kcal/kg
Now power developed in steam turbine P = Q X (H1-H2) / 860
Where Q is steam flow
P = 50 X (806.5-677) / 860
P = 7.52 MW
Note: 860 kcal = 1 KWH
2. Calculate the power developed by a steam turbine by using following data
Sl No.
Particular
UOM
Value
1
Turbine inlet steam flow
TPH
145
2
Turbine inlet steam pressure
Kg/cm2
88
3
Turbine inlet steam temperature
C0
515
4
Bleed steam flow
TPH
20
5
Bleed steam pressure
Kg/cm2
12
6
Bleed steam temperature
C0
250
7
Extraction flow
TPH
100
8
Extraction steam pressure
Kg/cm2
1.8
9
Extraction steam temperature
C0
145
10
Exhaust flow to condenser
TPH
25
11
Exhaust pressure
Kg/cm2
0.08
12
Exhaust temperature
C0
44
13
Dryness fraction
%
90

Also calculate the specific steam consumption of this Turbine
Solution:
Note down the enthalpy of steam at various stages
Turbine inlet steam enthalpy H1 = 818 kcal/kg
Bleed steam enthalpy H2 =700 kcal/kg
Extraction steam enthalpy H3 = 657.2 kcal/kg
Exhaust enthalpy =Liquid heat + Dryness fraction X Vapour enthalpy = 41.77 + 0.9 X 615.5 = 595.72 kcal/kg
Also steam flow is given
Inlet steam flow Q1 = 145 TPH
Bleed steam flow Q2 = 20 TPH
Extraction steam flow Q3 =100 TPH
Exhaust steam flow Q4 = 25 TPH
Power generation at 1st stage (Bleed) P1 = Q2 X (H1-H2) / 860
P1 = 20 X (818-700) / 860 = 2.74 MW
Power generation at 2nd stage (Extraction) P2 = Q3 X (H1-H3) / 860
P2 = 100 X (818-657.2) / 860 = 18.69 MW
Power generation at 3rd stage (Exhaust) P3 = Q4 X (H1-H4) / 860
P3 = 25 X (818-595.72) / 860 = 6.46 MW
SO total power developed at Turbine shaft P = P1+P2+P3 = 2.74+18.69+6.46 = 27.89 MW
Specific steam consumption SSC = Turbine inlet steam flow / Power generation = 145 / 27.89 =5.19 MT/MW

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3-By taking above example, explain how pure condensing steam Turbines have higher power generation & lower specific steam consumption (SSC)
Consider the above example, where Turbine inlet steam flow is 145 TPH & having 25 TPH exhaust steam flow to condenser.
If we condense 100% steam, then we will have reduced SSC
Let us see..
Q1=Q4=145 TPH..Where Q4 = Exhaust steam to condenser
Q2 & Q3 are considered zero (No flow)
Enthalpy of exhaust steam increases due to higher exhaust pressure
SO, Consider exhaust pressure = 0.1 kg/cm2 & Dryness fraction 0.9
Then, exhaust enthalpy becomes H1 = 46 + 0.9 X 617 = 601.9 kcal/kg
Total Power developed P= Q1 X (H1-H4) / 860
P =145 X (818-601.9) / 860 = 36.43 MW
So SSC = 145 / 36.43 = 3.98 MT/MW
This is very less as compared to bleed & extraction turbines

It's all about HP HEATERS

4-By taking an example No.2 explain how bleed steam flow will cause reduction in net power consumption
Solution:
We shall take the data of Example No.2
In this, we will increase bleed steam flow, pressure & temperature & parallel shall decrease extraction flow to match mass flow
Sl No.
Particular
UOM
Value
1
Turbine inlet steam flow
TPH
145
2
Turbine inlet steam pressure
Kg/cm2
88
3
Turbine inlet steam temperature
C0
515
4
Bleed steam flow
TPH
30
5
Bleed steam pressure
Kg/cm2
15
6
Bleed steam temperature
C0
285
7
Extraction flow
TPH
90
8
Extraction steam pressure
Kg/cm2
1.8
9
Extraction steam temperature
C0
145
10
Exhaust flow to condenser
TPH
25
11
Exhaust pressure
Kg/cm2
0.08
12
Exhaust temperature
C0
44
13
Dryness fraction
%
90

Solution:
Note down the enthalpy of steam at various stages
Turbine inlet steam enthalpy H1 = 818 kcal/kg
Bleed steam enthalpy H2 =716.63 kcal/kg
Extraction steam enthalpy H3 = 657.2 kcal/kg
Exhaust enthalpy =Liquid heat + Dryness fraction X Vapour enthalpy = 41.77 + 0.9 X 615.5 = 595.72 kcal/kg
Also steam flow is given
Inlet steam flow Q1 = 145 TPH
Bleed steam flow Q2 = 30 TPH
Extraction steam flow Q3 =90 TPH
Exhaust steam flow Q4 = 25 TPH
Power generation at 1st stage (Bleed) P1 = Q2 X (H1-H2) / 860
P1 = 30 X (818-716.63) / 860 = 3.53 MW
Power generation at 2nd stage (Extraction) P2 = Q3 X (H1-H3) / 860
P2 = 90 X (818-657.2) / 860 = 16.82 MW
Power generation at 3rd stage (Exhaust) P3 = Q4 X (H1-H4) / 860
P3 = 25 X (818-595.72) / 860 = 6.46 MW
SO total power developed at Turbine shaft P = P1+P2+P3 = 3.53+16.82+6.46 = 26.81 MW
Specific steam consumption SSC = Turbine inlet steam flow / Power generation = 145 / 26.81 =5.41 MT/MW
So by increasing the bleed steam flow, the work done by the Turbine decreases & hence steam consumption will increase

Read Steam Turbine commissioning

5-A Turbine’s inlet steam enthalpy is 825 kcal/kg & Exhaust enthalpy is 590 kcal/kg. Calculate the work done by steam & specific steam steam consumption
We have,
H1 = 825 kcal/kg, H2 = 590 kcal/kg
Work done per kg of steam = (H1-H2) = 825-890 =235 kcal/kg
SSC = 860 / Work done = 860 / 235 =3.65 kg/kwh or 3.65 MT/MW
6-A steam Turbine inlet steam pressure & temperatures are 104 kg/cm2 & 540 C0 & exhausts at pressure 0.09 kg/cm2 & temperature 43 Deg C calculate the
a-      Work done per kg of steam
b-      Heat supplied per kg of steam
c-       Cycle efficiency
Enthalpy of inlet steam = 829 kcal/kg
Exhaust liquid enthalpy = 44 kcal/kg
Exhaust enthalpy by considering 90% dryness fraction = 44 + 0.9 X 616.44 =598.76 kcal/kg
A-Work done per kg of steam = (829-598.76) = 230.24 kcal/kg
B-Heat supplied per kg of steam = 829-44 = 785 kcal/kg
C-Cycle efficiency = Work done per kg of steam X 100 / Heat supplied per kg of steam
                                 = 230.24 X 100 / 785 = 29.32%
Note:
Power developed at Generator terminals = Power developed at Turbine Shaft X Reduction gear box efficiency X Alternator efficiency
For example:
Calculate the net power developed at Generator terminal if 100 TPH steam enters the Turbine at 811 kcal/kg enthalpy & leaves the Turbine at enthalpy 565 kcal/kg .Assume Gear box efficiency as 98% & Generator efficiency as 95%
Power developed on Turbine shaft = 100 X (811-565) / 860 = 28.0 MW
Net power developed at Generator output terminals = 28.0 X 0.98 X 0.95 = 26.06 MW

Also read vacuum troubleshooting in steam Turbines

Power generation phenomenon in STG set



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