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As can be seen it is very important to have a good steam quality. I.e. = 1.

Therefore slight superheating is recommended.

For instance if X=0.5 instead of 1, the steam consumption will increase with a factor 2. I.e.the machine acts as if 50% of the flow is by-passed.

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

Effect of inlet steam quality X if the inlet steam mass flow is constant.

 

This is an addition to the data file “Importance of having good steam quality x at the inlet of a Steam Screw Expander generating electric power” earlier uploaded on Research Gate

In these calculations the steam mass flow is kept constant by changing the inlet pressure and temperature. As can be seen the generated power as well as the inlet pressure decreases with decreasing inlet steam quality.

 

Other data are:

Rotor diameter = 200 mm

Inlet/Outlet pressure = 8/1 bar at steam quality = 1.0

Inlet/Outlet temperature 170.4/99.6 centigrade at steam quality = 1.0

 

Inlet steam mass flow = 7.2 ton/h in all calculations.

 

Built in volume ratio =1.0.

By having this value effects from flashing or condensation are outside the control volume. I.e. they can be neglected

Male rotor tip speed = 60 m/s

Generator efficiency = 0.95 

 

Fig.1 shows that the generated effect decreases with decreasing steam quality. 

   

  

Fig. 1

 

This is due to the decrease in inlet pressure, See fig.2.

 

Fig. 2

 

Fig. 3 shows the decrease of inlet pressure and generated electric power.

As is obvious from these calculations the inlet quality is an important parameter,

 

 

Fig. 3

        

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Importance of having good steam quality x at the inlet of a Steam Screw Expander generating electric power.

 

 From fig 1 it can be seen that the generated effect is approximately the same for steam quality x > 0.2.
It is also interesting to see that for x > 0.2 most of the volume in the screw expander is filled with pure steam, which explains the almost constant generated effect.
The water volume is very small.
 Example:
 x=0.25
Steam = 98.63 % of total volume
Water = 1.37 % of total volume 
   
------------------
Other data are:
Rotor diameter = 200 mm
Inlet/Outlet pressure = 8/1 bar
Inlet/Outlet temperature 170.4/99.6 centigrade
 Built in volume ratio =1.0.
Male rotor tip speed = 60 m/s
Generator efficiency = 0.95
  

Fig. 1

This looks very nice, but a look at fig.2 below shows that the steam consumption is very dependent of the steam quality x.

For example if you decrease the steam quality from 1 to 0.5 the steam mass flow increases twice.

 

Fig. 2

        

­­­­­­­­­­­­­­­­­­­-------------------------------------------------------------------­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ 

 

Effect of built-in volume ratio at different steam quality X upon the performance of aTwin Screw Steam Expander driving a generator producing electrical power. 

In order to give more information about the effects of various built-in ratio at different steam quality X_, when using a screw expander for generating electrical power these calculations are presented. 

The expander is a dry twin screw expander with synchronizing bearings

Profile = 4+6-combination

Male rotor diameter = 285 mm

Female rotor diameter = 285 mm.

Male rotor tip velocity = 60 m/s

Inlet pressure = 5 bar.

Inlet temperature = 151.85 centigrade

Outlet pressure = 1bar

The quality x noted in the graphs are values at the screw expander inlet. 

Generator efficiency = 95 %

Calculation results:

The presented data sets below show the following:

Fig.1 shows the generated electrical power as a function of built-in volume ratio at various steam quality X.

Fig.2 shows the mass flow through the expander.

Fig.3 shows the generated specific power.

 

Fig. 1. Generated electrical power as a function of built-in volume ratio.

As can be seen the generated power is about the same for quality 0.10 < x < 1.

Notice that at x=0.0 the generated power is drastically decreased due to high inlet

pressure drop caused by the water quality x=0.

  

Fig. 2. Mass flow through expander as a function of built-in volume ratio. 

As is obvious the mass flow through the screw expander increases with decreasing quality x.

   

 

Fig. 3. Generated specific power as a function of built-in volume ratio. 

The generated specific power is calculated: (generated power [kW])/ (mass flow through expander [kg/s]). 

Conclusion

It is quite obvious that it is important to have a high quality x.

     

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

  ORC-system 

Effect of different built-in volume ratio upon the performance of an ORC-system,

which uses a helical screw expander for driving a generator producing electrical power.

In order to give more information about the effects of various built-in volume ratio V_i, when using a screw expander in an ORC-system these calculations are presented.

The presented graph  presents the performance as a function of the brine flow.

The expander is a dry screw expander with synchronizing bearings

Rotor diameter = 285 mm.        

Built in volume ratio = 3 cases, namely 1, 2, 3.

The optimized built-in volume ratio in this case = 3 

Male rotor tip speed is from 30 m/s up to 120 m/s

Working media = R236fa

Quality x = 1.0 at the screw expander inlet.  

Brine = Water

Coolant = Water

Brine temp = 100 centigrade

Coolant temp = 20 centigrade  

Evaporation temp. = 90 centigrade

Condensing temp. = 30 centigrade

Pump losses in ORC system are included.

Brine pump losses are not included.

Coolant pump losses are included. 

Fluid pump efficiency = 0.7 

Temp. efficiency (preheater+evaporator)  = 0.9

Temp. efficiency condensor = 0.9

 Generator efficiency = 0.95

Calculation results:

As can be seen from the graph the built-in volume ratio = 1 gives the highest production of power, but the ORC-efficiency is not so high.

At V_i=3 the ORC-efficiency is highest at brine flow = 72 ton/hour

ORC-efficiency = 8.3 %

Generated power = 433 kW

Performance as a function of brine flow

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­     

Effect of feed pump power consumption at different steam quality X on the generated power from a R134a ORC-system using a Twin Screw Expander.

-----------------

Brine = Water
Coolant = Water

Working medium =R134a, 0.0 < x <1.0 at the expander inlet

Built-in volume ratio =2.0

NOTE: This built-in volume ratio is then used in all calculations

Rotor diameter = 285 mm

Male rotor tip speed = 60 m/s

Brine temp in = 100 centigrade

Coolant temp in = 20 centigrade

Evaporation temp = (11*Brine temp + 5*Coolant temp)/16 = 95.625 centigrade

Evaporation pressure = 23.641 bar
Condensing temp = (3*Brine temp + 13*Coolant temp)/16 = 40.625 centigrade

Condensing pressure = 8.8698 bar

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.
Temp. efficiency Evaporator = 90 %
Temp. efficiency Condenser = 90 %

---------------------------------------------------------------------------------------------------------------------------------

Fig 1 shows the mass flow, feed pump consumption, shaft power and the generated electricity.

As you can see decreasing quality X increases the mass flow, which also leads to increased feed pump power consumption.

At steam quality close to zero the losses caused by the feed pump are higher than the generated shaft power.

As is obvious it is important to have a good quality x at the expander inlet. 

Fig.1 

        

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Screw Expander Inlet Pressure Drop and it’s Effect on

Performance as a function of R245fa inlet quality X

 

Input data:

Brine = Water
Coolant = Water 

Working medium =R245a, 0.2 < x <1.0 at the expander inlet

Built-in volume ratio =2.5, Optimized at X=1.0
NOTE: This built-in volume ratio is then used in all calculations

Rotor diameter = 285 mm
Male rotor tip speed = 60 m/s

Brine temp in = 120 centigrade
Coolant temp in = 20 centigrade 

Evaporation temp = (11*Brine temp + 5*Coolant temp)/16 = 99.625 centigrade
Evaporation pressure = 11.46 bar 

Condensing temp = (3*Brine temp + 13*Coolant temp)/16 = 40.625 centigrade
Condensing pressure = 2.5567 bar

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.
Temp. efficiency Evaporator = 90 %
 Temp. efficiency Condenser = 90 %

---------------------------------------------------------------------------------------------------------------------------------

Fig 1 shows the pressure drop across the screw expander inlet port during the filling phase.
As is obvious the pressure drop is high at the opening and the closing of the inlet port due to the small areas.

Fig 1

Fig 2 shows the shaft power as well as the filling and the adiabatic efficiency.
 As you can see all these parameters decrease when the quality X at the expander inlet decreases.
As is obvious it is important to have a good quality x at the expander inlet. 

Fig 2
---------------------------------------------------------------------------------------------------------------------------------

Fig 3 shows the generated power in an ORC-systemas well as the filling and the ORC-efficiency.
 As you can see all these parameters decrease when the quality X at the expander inlet decreases.
As is obvious it is important to have a good quality x at the expander inlet. 
 

 

Fig 3

                  

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    SOLAR COLLECTORS

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

                   Influence of channel shape on Solar Collector Performance

PICTURE BELOW:

Expose the upper side to incoming heat from the sun and then cover the end of the flanges you get many boxes.
Then flow air through the channels you will get a very good heat transfer to the air because:
- You have good heat conduction in the flanges
- You increase the heat transfer surface when the ratio (length of flange/distance between flanges) increases
- The heat transfer is more efficient the closer the flanges are

Length of flange = 135 mm
Distance between flanges = 20 mm



Here are examples of some standard designs that one can buy.

       


See also:
 
https://www.researchgate.net/publication/301551572_Addition_to_Influence_of_channel_shape_on_Solar_Collector_Performance

https://www.researchgate.net/publication/299599242_Influence_of_channel_shape_on_Solar_Collector_Performance

   

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SCREW COMPRESSORS/EXPANDERS

Estimated Performance of a Waste Heat Recovery System

Stage 1: Steam Screw Expander

Stage 2: ORC using Screw  Expander

 

 

Stage 1: Steam Screw Expander in above Combined System

 

 

Stage 2: ORC using Screw Expander in above Combined System

    

 

Change the working medium in stage 2 from R134a to R245fa.

Then it is necessary to change the rotor diam. from 285 mm to 403 mm

to get the same performance.

Why not use a turbine instead, since the expansion takes place in the superheated region?

Any objections? 

   

  

In connection with this the following might be of interest: 
 
http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2442&context=iracc
  
Now I changed the second stage from Screw Expander to a R245faTurbine.
The performance is the same, but the turbine is a smaller machine than a Screw Expander.
. 

 
The article:

Performance characteristics of a 200-kW organic Rankine cycle system in a steel processing plant by
Taehong Sung a, Eunkoo Yun a,b, Hyun Dong Kim a, Sang Youl Yoon a, Bum Seog Choi c, Kuisoon Kim a, Jangmok Kim a, Yang Beom Jung d, Kyung Chun Kim a,⇑

is an interesting example for the second stage.
Can be found on Research Gate.

  

 

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Using two Helical Screw Expanders of same size for generation of Power from a 2 stage Heat Recovery System

Stage 1: Steam Screw Expander, Diam. = 285 mm

Stage 2: ORC using R245fa Screw Expander, Diam. = 285 mm 

The two screw expanders in this system are dry expanders of the same size, namely diam. = 285mm.
The tip speeds: Steam expander 41.5 to 124.5 m/s, R245fa expander 30 to 60 m/s 

 Fig.1 shows the generated effect as a function of the steam flow entering the system.
 

Fig.1

Stage 1: Steam Screw Expander in above Combined System

Rotor diameter = 285 mm
Built-in volume ratio = 2.0

Inlet/Outlet pressure = 5/1 bar
Inlet/Outlet temperature 151.8/99.6 centigrade

Male rotor tip speed = 41.5 < Vtip < 124.5 m/s
Generator efficiency = 0.95

Fig.2 shows that the generated effect and the adiabatic efficiency as a function of the steam flow leaving the steam expander.
  

Fig.2

Stage 2: ORC using Screw Expander in above Combined System

Rotor diameter = 285 mm
Built-in volume ratio = 1.9
Male rotor tip speed = 41.5 < Vtip < 124.5 m/s

Brine = Water of steam quality x=0.92 leaving the steam expander stage 1
Coolant = Water

Brine temp in = 100 centigrade
Coolant temp in = 20 centigrade

Working medium =R245fa
R245fa quality x at expander inlet = 1.0

Evaporation temp = (11*Brine temp + 5*Coolant temp)/16 = 75 centigrade
Evaporation pressure = 6.9510 bar
Condensing temp = (3*Brine temp + 13*Coolant temp)/16 = 35 centigrade
Condensing pressure = 2.1172 bar

Temp. efficiency Evaporator = 90 %
Temp. efficiency Condenser = 90 %

Generator efficiency = 0.95

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.

Fig 3 shows generated power and ORC-efficiency.
  

Fig.3

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ 

 

Improvement of

“Using two Helical Screw Expanders of same size for generation of Power from a

2 stage Heat Recovery System”

 

 Stage 1: Steam Screw Expander, Diam. = 285 mm

Stage 2: ORC using R245fa Screw Expander, Diam. = 285 mm 

The two screw expanders in this system are dry expanders of the same size, namely diam. = 285mm.

Tip speeds: Steam expander 41.5 to 124.5 m/s, R245fa ORC-expander 30 to 90 m/s 

 Fig.1 shows the generated effect as a function of the brine flow in the system.

Fig.1.

 

Stage 1: Steam Screw Expander in above Combined System

 

Rotor diameter = 285 mm

Built-in volume ratio = 2.0

 

Inlet/Outlet pressure = 5/1 bar,

Inlet/Outlet temperature 151.8/102.9 centigrade

 

Male rotor tip speed = 41.5 < Vtip < 124.5 m/s

Generator efficiency = 0.95 

Fig.2 shows that the generated effect and the adiabatic efficiency as a function of the brine (steam) flow leaving the steam expander.

Fig.2

 

Stage 2: ORC using Screw Expander in above Combined System  

Rotor diameter = 285 mm

Built-in volume ratio = 1.9

Male rotor tip speed = 30 < Vtip < 90 m/s

 

 

Brine = Steam of temperature 102.9 centigrade leaving the steam expander stage 1
Coolant = Water                                                                                                     

 

Brine temp in = 102.9 centigrade

Coolant temp in = 20 centigrade

 

Working medium =R245fa

R245fa quality x at expander inlet = 1.0

 

Evaporation temp = 85 centigrade

Evaporation pressure = 8.9278 bar
Condensing temp = 35 centigrade

Condensing pressure = 2.1172 bar

 

Temp. efficiency (Evaporator +Preheater) = 90 %
Temp. efficiency Condenser = 90 %

 

Generator efficiency = 0.95

 

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included. 

Fig 3 shows generated power and ORC-efficiency.

Fig.3

           

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­  

Increased brine flow and decreased output of electrical power due to decreased R245fa steam quality x from an ORC-system using a Twin Screw Expander.

 

This graph is just to show the importance of having a good steam quality at the screw expander inlet.

One can say that this is typical for all displacement machines - not only screw expanders.

 

-----------------

Brine = Water
Coolant = Water

 

Working medium =R245fa

 

R245fa quality x at expander inlet = 1.0, 0.5 and 0.25

Built-in volume ratio = 1.9, Optimized at x=1.0

 

Rotor diameter = 285 mm

 

Brine temp in = 100 centigrade

Coolant temp in = 20 centigrade

 

Evaporation temp = (11*Brine temp + 5*Coolant temp)/16 = 75 centigrade

Evaporation pressure = 6.9510 bar
Condensing temp = (3*Brine temp + 13*Coolant temp)/16 = 35 centigrade

Condensing pressure = 2.1172 bar

 

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.
Temp. efficiency Evaporator = 90 %
Temp. efficiency Condenser = 90 %

---------------------------------------------------------------------------------------------------------------------------------

  
Fig 1 shows the generated power and ORC-efficiency. As you can see all these parameters decrease when the quality X at the expander inlet decreases.

As is obvious it is important to have a good quality x at the expander inlet. 

    

Fig. 1  

  

­­­­­­­­­­­­­­­­­­­-------------------------------------------------------------------­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ 

  

Adjusting of Steam Screw Expander rotor tip speed in order to keep the inlet mass flow constant at different inlet steam quality X.

 

This is an addition to the data file “Importance of having good steam quality x at the inlet of a Steam Screw Expander generating electric power” and “Effect of inlet steam quality X if the inlet steam mass flow is constant”.

In these calculations the steam mass flow is kept constant by changing the male rotor tip speed at different steam quality x.

As can be seen the generated power decreases with decreasing inlet steam quality x.

 

Other data are:

Rotor diameter = 200 mm

Inlet/Outlet pressure = 8/1 bar at all calculated steam quality points

Inlet/Outlet temperature 170.4/99.6 centigrade at all calculated steam quality points

 

Inlet steam mass flow = 2.05 ton/h in all calculations.

 

Built-in volume ratio = 3.2, optimized at steam quality x =1.0

Generator efficiency = 0.95

 

Fig.1 shows that the generated effect decreases with decreasing steam quality.

Fig. 1

 

Fig. 2 shows the variation of the male rotor tip speed to get the inlet steam mass flow to be constant,

 

Fig. 2 

           

­­­­­­­­­­­­­­­­­­­-------------------------------------------------------------------­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ 

  

 

New version of Effect of inlet steam quality X if the inlet steam mass flow is constant.

 

This is an addition to the data file “Importance of having good steam quality x at the inlet of a Steam Screw Expander generating electric power” and “Effect of inlet steam quality X if the inlet steam mass flow is constant” earlier uploaded on Research Gate

In these calculations the steam mass flow is kept constant by changing the built-in volume ratio.

As can be seen the generated power and the filling decreases with decreasing inlet steam quality. The adiabatic efficiency is maximum at x=3.0

Other data are:

Rotor diameter = 200 mm

Inlet/Outlet pressure = 8/1 bar at all calculated steam quality points

Inlet/Outlet temperature 170.4/99.6 centigrade at all calculated steam quality points

  

Inlet steam mass flow = 7.2 ton/h in all calculations.

  

Male rotor tip speed = 60 m/s

Generator efficiency = 0.95 

  

Fig.1 shows that the generated effect and the filling decreases with decreasing steam quality.

The adiabatic efficiency is maximum at x=0.3.

   

Fig. 1

 

Fig. 2 shows the variation of the built-in volume ratio to get the inlet steam mass flow to be constant

   

Fig. 2

    

­­­­­­­­­­­­­­­­­­­-------------------------------------------------------------------­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ 

  

 

Effect of steam quality X upon the performance of an ORC-system,

which uses a screw expander for driving a generator producing electrical power

In order to give more information about the effects of various steam quality X_, when using a screw expander in an ORC-system these calculations are presented.

This data set presents 2 graphs, where fig.1 shows the performance as a function of the male rotor tip speed and fig.2 the performance as a function of the brine flow.

The expander is a dry screw expander with synchronizing bearings

Rotor diameter = 285 mm

Built in volume ratio = 1.8, which is optimized at male rotor tip speed = 60 m/s

Brine = Water

Coolant = Water

Brine temp = 90 centigrade

Coolant temp = 20 centigrade

Evaporation temp. = (11*Brine temp + 5*Coolant temp)/16 = 68.125 centigrade

Condensing temp = (3*Brine temp + 13*Coolant temp)/16 = 33.125 centigrade

These temperatures are valid for all presented calculations.

Pump losses in ORC system are included.

Brine pump losses are not included.

Coolant pump losses are included.

Temperature efficiency Evaporator = 90 %

Temperature efficiency Condenser = 90 %

Working media = R134a

Generator efficiency = 95 %

Calculation results:

As can be seen from fig. 1 and 2 the generated power decreases with decreasing quality X.

 

Fig. 1. Performance as a function of male rotor tip speed

 

Fig. 2. Performance as a function of brine flow

     

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­     

  

Effect of different built-in volume ratio upon the performance of an ORC-system,

which uses a helical screw expander for driving a generator producing electrical power.

  

In order to give more information about the effects of various built-in volume ratio V_i, when using a screw expander in an ORC-system these calculations are presented.

This data set presents 2 graphs, where fig.1 shows the performance as a function of the male rotor tip speed and fig.2 the performance as a function of the brine flow.

 

The expander is a dry screw expander with synchronizing bearings

Rotor diameter = 285 mm             

Built in volume ratio = 3 cases, namely 1, 2, 3

 

Brine = Water

Coolant = Water

Brine temp = 90 centigrade

Coolant temp = 20 centigrade  

 

Evaporation temp. = (11*Brine temp + 5*Coolant temp)/16

Condensing temp = (3*Brine temp + 13*Coolant temp)/16

These temperatures are valid for all presented calculations.

 

Pump losses in ORC system are included.

Brine pump losses are not included.

Coolant pump losses are included. 

 

Working media = R134a

Quality x = 1.0 at the screw expander inlet  

Calculation results:

As can be seen from fig. 1 the built-in volume ratio = 1 gives the highest production of power, but the ORC-efficiency is not so high.

At V_i=2 the produced power is lower, but now the efficiency has increased and is very close to the optimized V_i=1.8.

At V_i=3 the produced power begins to decrease after male rotor tip speed = 80 m/s.

 Please note that the ORC-efficiency decreases when the tip speed increases.

This is due to the increased pressure drop at the expander inlet.

 

Fig. 1. Performance as a function of male rotor tip speed

As can be seen from fig.2 the operational range is strongly reduced when V_i is increased.

For Vi = 3 the pressure drop loss at the inlet is so high that the operational range is extremely reduced.

At brine flow above 130 m³/h the generated effect starts to decrease. 

 

Fig. 2. Performance as a function of brine flow

       

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 Influence of different built-in volume ratio on the generated power from of an ORC, using

a screw expander for driving a generator producing electrical power.

  

In order to give more information about the effects of various built-in volume ratio V_i, when using a screw expander in an ORC-system these calculations are also presented.

The presented graph shows the generated power and the ORC-efficiency a function of the brine flow.

 

The expander is a dry screw expander with synchronizing bearings

Rotor diameter = 285 mm

Male rotor tip speed is from 30 m/s up to 110 m/s.              

The present results are for built-in volume ratio 1, 2 and 3

 

Brine = Water

Coolant = Water

Brine temp = 130 centigrade

Coolant temp = 20 centigrade  

 

Evaporation temp. = (11*Brine temp + 5*Coolant temp)/16

Condensing temp = (3*Brine temp + 13*Coolant temp)/16

These temperatures are valid for all presented calculations.

 

Pump losses in ORC system are included.

Brine pump losses are not included.

Coolant pump losses are included. 

 

Working media = R236fa

Quality x = 1.0 at the screw expander inlet  

Calculation results:

As can be seen from the graph the built-in volume ration Vi = 1 gives the highest production of power but the ORC-efficiency is not so high.

At Vi =2 the produced power is lower, but now the ORC-efficiency has increased.

At Vi =3 the produced power is even more low and the ORC-efficiency as high as 7.6 % at 60 m3/h brine flow.

The operational range is strongly reduced when Vi is reduced.

 

Performance as a function of brine flow

     

BoSångfors Consulting, Sweden 

This picture shows the effect of using saturated steam instead of water.

As can be seen the use of saturated steam is much more efficient than the use of water.

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 Influence of different working medium on ORC Performance

Brine = water

Coolant = water

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 Effect of Brine outlet temperature on the needed Brineflowin an ORC-systeem using a Twin Screw Expander 

As is well known it is important to have a good heat transfer from the brine to the working media.

The intention of this short data set is to show how the brine outlet temperature effects the needed brine flow.

-----------------

Brine = Water
Coolant = Water 

Working medium =Ammonia, x=1.0 at the expander inlet 

Built-in volume ratio =2.0

Rotor diameter = 285 mm

Male rotor tip speed = 60 m/s

Brine temp in = 100 centigrade

Coolant temp in = 20 centigrade 

Evaporation temp = 80 centigrade                  Evaporation pressure = 41.42 bar
Condensing temp = 30 centigrade                 Condensing pressure = 11.67 bar 

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.
Temp. efficiency Evaporator = 25-100 %
Temp. efficiency Condenser = 90 %

Generated power = 1397.7 kW

ORC-efficiency = 8.00 %

--------------------------------------------------------------------------------------------------------------------------------- 

Fig 1 shows the needed brine flow as a function of the brine outlet temperature.

As is obvious it is important to have preheater and evaporator with good heat transfer. 

Fig.1   

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Effect of not having the right coolant flow upon the performance of an ORC-system when using a screw expander.

Fig 1 and 2 show what happens if you change the brine flow but have the coolant flow constant. As is obvious it is important to have enough coolant flow if you want an efficient ORC performance. 

Brine = Water
Coolant = Water

Working medium =R134a, x=1.0 at expander inlet
Built in volume ratio =1.8

Brine temp in = 90 degr.C
Brine flow : See fig 1 and fig 2. 

Coolant temp in = 20 degr.C
Coolant flow =  See fig 2. Showing the perfect and the unchanged condition

R134a, x=1.0
Built in volume ratio =1.8

Brine temp in = 90 degr.C
Brine flow : See graph

Evaporationtemp = (11*Brinetemp + 5*Coolanttemp)/16
Condensingtemp = (3*Brinetemp + 13*Coolanttemp)/16

This value of the condensing temp. is valid for the perfect condition.

At constant cooling flow see fig 2.
Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.
Temp. efficiency Evaporator = 90 %
Temp. efficiency Condenser = 90 % 

Fig.1  

Fig.2

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Fig 1 shows what happens if you change the steam quality x at the inlet of the screw expander. As you can see the generated power as well as the ORC-efficiency decreases as x decreases, but the brine flow increases.

As is obvious it is important to have a good quality x at the expander inlet.

Brine = Water
Coolant = Water

Working medium =R245a, 0.2 < x <1.0 at the expander inlet
Built-in volume ratio =2.0, NOTE: This is the optimized built-in volume ratio in all calculations

Rotor diameter = 403 mm

Male rotor tip speed = 54 m/s

Brine temp in = 100 centigrade

Coolant temp in = 20 centigrade

Evaporation temp = (11*Brine temp + 5*Coolant temp)/16 = 75 centigrade

Evaporation pressure = 6.95 bar
Condensing temp = (3*Brine temp + 13*Coolant temp)/16 = 35 centigrade

Condensing pressure = 2.12 bar

Pump losses in ORC system are included.
Brine pump losses are not included.
Coolant pump losses are included.
Temp. efficiency Evaporator = 90 %
Temp. efficiency Condenser = 90 %

Fig 1 

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Effect of change of Steam Quality X in a Steam Screw Expander 

In order to find out the effect of the variation of Steam Quality in a screw expander this investigation was made.It is assumed that the change is immediate. I.e. no time factor is taken into consideration, which means that the presented effect is maximum.

The values for the steam quality are taken from the program Refprop. 

Example:

Steam flow = 8 ton/h.

Reduction of power compared to not corrected:

Assumed adiabatic efficiency  70 % = 2.0 %

Assumed adiabatic efficiency 100 % = 3.5 %

Fig.1

Fig.2

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BoSångfors Consulting, Sweden 

Leakage analysis of a Twin Screw Compressor.

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BoSångfors Consulting, Sweden 

Leakage analysis of a Twin Screw Expander.

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 Edstroem Consulting, Sweden

Prediction of pressure in the manifold between Supercharger and Engine in the case of

back-fire.

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  BoSångfors Consulting, Sweden

Effect of water injection into the first stage of a two-stage screw compressor unit 

 These computer simulations are using a modified theory of that described in the papers:

“Computer Simulation of Effects from Injection of Different Liquids in Screw Compressors”, Purdue 1998“ and

 "Numerical calculation of effects from injection of different liquids in twin screw compressors”, VDI 1998.

The results of the presented calculations show that at water injection rate 67.3 lit/min to the 2nd stage

 and 37 lit/min to the 1st stage gives reduced power consumption.    

Further increase of the 1st stage water injection rate does not improve the performance very much.       

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

 LEWD Engineering, Sweden

Influence of water injection on outlet parameters after a radial supercharger.

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ALSTOM K.K., Japan,

ALSTOM Power Energy Recovery GmbH, Germany:

Kobe University, Kobe, Japan

Cleaning of Flue Gas from CO₂

by the use of lithium silicate (Li₄SiO₄) coated on

the heat transfer elements in a rotary

heat exchanger. 

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 BoSångfors Consulting, Sweden

               Calculated Performance of a Rotary Heat Exchanger during start-up in a Power Plant   

NOTE: When  the flue gas contains for instance sulphuric acid it is necessary to start with high excess air. By doing that you get a smaller concentration of sulphuric acid in the flue gas and a lower condensation temperature. Then you avoid condensation deep into the heat transfer elements.

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 BoSångfors Consulting, Sweden

Temperatures and Water content in Regenerative resp. Recuperative Heat Exchanger operating under water dew point.

Inlet condition = Flue gas with water spray injection.

Flue gas inlet temperature = Water dew point temperature   

Please also look at: http://www.freepatentsonline.com/5482108.html

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BoSångfors Consulting, Sweden  

Leakage analysis of a Tri-sector Rotary Heat Exchanger.

Rotor diameter = 8.283 m

Rotor height = 2.143 m

Rotor speed = 2 rpm

Element porosity = 0.84

Flue gas flow = 454183 kg/h

Air sector primary = 30 degree.

Air sector secondary = 150 degree.

Gas sector = 180 degree.

PRESSURES [Pa]

Air in primary P1= 11442

Air out primary P2= 11234

Air in secondary P1s= 2179

Air out secondaryP2s= -79

Gas in P3= -497

Gas out P4 = -1942

CIRCUMFERENTIAL SEAL CLEARANCES [mm]

Primary in S1= 1

Primary out S2= 1

Secondary in S1s=1

Secondary outS2s=1

Gas in S3=1

Gas out S4=1

TEMPERATURES [degr.C]

Air in primary T1=50

Air out primary T2=372

Air in secondary T1s=55

Air out secondary T2s=357

Gas in T3=390

SECTOR PLATE CLEARANCES [mm]

Cold end =2

Hot end =2

NOMENCLATURE (diagrams)

pma = pressure in volume between casing and rotor, primary air [Pa]

pmas = pressure in volume between casing and rotor, secondary air [Pa]

pmg = pressure in volume between casing and rotor, gas [Pa]

m1 = flow over circumferential seal primary inlet air [kg/h]

m2 = flow over circumferential seal primary outlet air [kg/h]

mps = flow over axial seal from primary to secondary [kg/h]

m1s = flow over circumferential seal secondary to gas [kg/h]

m2s = flow over circumferential seal secondary outlet air [kg/h]

msg= flow over axial seal from primary to gas [kg/h]

m3 = flow over circumferential seal inlet gas, [kg/h]

m4 = flow over circumferential seal outlet gas, [kg/h]

mg = flue gas flow [kg/h]

Air leak = Air leakage into gas [per cent of flue gas mass flow]

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BoSångfors Consulting, Sweden