Solid Waste Solutions

 

Update 10/19/2017 - Utility Power Generation using Engineered Fuel


The PennElec Boiler model employs a steady state Newton-Raphson algorithm with a Forward Euler algorithm for the Turbine and feedwater heaters molded into an integrated unit that conserves mass and energy.


Eight preliminary studies on PENELEC’S Unit 3 (Homer City) fossil fuel generating station at Homer City, PA. are complete whcih include the base and originial coal compositions for comparison.  All eight tests vary significantlyv in Carbon, Hydrogen, Oxygen and moisture content but were capable of adequately powering the PennElec Homer City plant.  However, only Case 8 had sufficient heat content to permit use of the existing (4.3) coal pulverizers without additional plant modifications. Data remains to be plotted for the eight cases.


Fuel

A model fuel composition more representative of the Pennelec plant was selected as the base fuel case for ongoing municipal waste combustion evaluation.

The Boiler base case credit and loss summary contains the model fuel composition and Boiler efficiency data. Model mass and energy balance validation data is now detailed in the Powerpoint presentation 'Evaluating Green Projects' - Syn Fuel from Municipal Waste, currently REV 'O'      


A Hardcopy of base case calculated results (Heatsum.prt) is available for download for the model calculated coal case conditions here.  See below for full test series data.


Case 8 Engr Fuel High Heating Value (HHV)

The High heating value for Case 8 is 14, 019 Btu/lb compared to 13,118 Btu/lb for the coal base reference. Case 8 defines a new solid waste fuel composition that is a blend of municipal waste and shredded automobile tires, sans the steel belting. It was intentionally formulated to be on the high end of heat content.  Unfortunately,  hydrogen content of waste fuel is large compared to conventional fossil fuels which requires changes in soot blowing time and duration.


Municipal waste fuels maycan be readily blended to match the heat content of coal producing less emissions provided the plant has added additional pulverizer capacity to handle a lower waste fuel heat content. 

Greater waste fuel combustion is precisely what is desired to rid municipalities of solid waste otherwise winding up in a landfil.  (All cases considered assume complete fuel combustion )


Note that fuel moisture includes the effect of humidity in the combustion air.


Case 8 Model Fuel Blend

The following EXCEL table contains the model fuel composition for Case 8 as determined by the Thermodynamic Approximation of Fuel Heat Content Table.

 

Basis EPA 2005 Tires 2017 Blend    
Split: 0.32 0.68      
  Waste Tires Composition H Btu/lb-mole Moles
C: 0.48 0.5794 0.5470 92703.82 0.0456
H: 0.0538 0.1558 0.1230 15145.06 0.0611
S: 0.0011 0.0464 0.0310 4063.29 0.0010
O: 0.26 0 0.0830   0.0052
N: 0.0034 0 0.0011   0.0000
H2O: 0.135 0.0510 0.0779   0.0028
Ash/solids: 0.068 0.1671 0.1370    
           
Total - lbs 1.001 1.000 1.000 111,912.17 0.1157
        36.55 cost per ton
        111,912 Btu/lb-mole
      AvgMol wt: 8.6 lb/lb-mole
      Density: 57.5 lbs/ft3
      HHV: 12950 Btu/lb
      Dulong: 15088 Btu/lb
      Avg HHV: 14019  

 

The waste Fuel composition is based on Table 1. Municipal Solid Waste (MSW) Heat Content and Biogenic/Non-Shares, 1989 - 2005 as noted in the Power Point presentation, Rev O.  Enthalpies of combustion were calculated for the MSW components (carbon, hydrogen, etc) and verified against EPA heat content data. Engineered fuel composition was calculated as a mass fraction of both MSW and Shredded rubber tires. The Dulong equation and the thermodynamic heat content, (Btu/lb) were averaged to predict the High Heating Value (HHV) of the Fuel.  This value appears in the fuel summary on Page One of the Model 'Unit Credit and Loss Summary'.


Boiler

 

Predicted power generation based on Case 8 fuel is 656.7 MW.  Superheater spray runs a bit closer to the coal case utilizing 33,501 lbs/hr versus 32,585 for the reference base.

Temperatures and pressures are equilvalent to the base case despite the lower carbon content. Unit operation for this case had to be modified to accomodate the fuel differences.  The Superheat and Reheat bank absorptions were allowed to slag up slightly at Kfs = .85, .85 and Kfr =.86, .86 respectively) for Case 8 down from .92+ for the base to give better temperature control at the Throttle and Reheat turbine inlets.  Overfire air was reduced to compenstate for the fuel's higher oxygen content.


When higher carbon content is available in the waste fuel, increased sootblowing will restore the effective absorbtivity of the superheat and reheat boiler banks


Case 8 is typical of waste fuel combustion in utility power generation. It's high hydrogen temperature makes reheat temperature more difficult to control.  The unit was somewhat sluggish due to the over 9% fuel moisture content. Typically fuel would not be combusted with moisture contents much over 2% but it was necessary to demonstrate that higher waste fuel moisture content could be accomodated in a conventional utility boiler. 


Industrial fluidized bed boilers can accomodate higher fuel moisture contents than utility boilers and are well suited to burning solid municipal wastes including sewage sludge.

Unit Heatrate for Case 8 was 10,293 Btu/KWH versus 10,292 Btu/KWH for the 100% coal base case, the heatrate performance difference between coal and the waste fuel was less than a quarter percent of normal unit operation.

The model utilizes an appoximation algorithm to estimate excess oxygen in the flue gas and Furnace Exit Gas (FEG) streams based on an oxygen balance. Case 8 shows less than a 2% difference in the two quantities.


Model Material & Energy Balance

 

Feedwater to the Boiler is 4491687 lbs/hr feedwater versus 4493358 lb/hr feedwater for the base case.  The difference is neglible.


Case 8 Steam Conditions



The Pennsylvania Electric Homer City Unit 3 typically consumes approximately 1,600,000 tons of compliance coal per year.  The plant purchases approximately 75% of this coal from one supplier and that coal is blended at a coal blending facility owned by the supplier. The remainder of the coal needed for Unit 3 is obtained in the spot market. - http://www.getfilings.com/o0000912057-02-012778.html  Subsequent Unit 3 equipment improvements are not modeled and model architecture has been adjusted so fuel combustion operations are closer to Homer City’s original commissioning. 

Be sure and ask the EPA and its climate modelers for the model validation data that justifys their global warming predictions before trusting in their conclusions.


Turbine:

 

The Pennelec Turbine is a GE 700 MW four valve unit operating in sliding (or variable) pressure mode (99.9% open) with single state reheat.  The boiler is fired for temperature in all model case runs. The generator is Hydrogen cooled at 60 psi with Demineralized water heat exchange for stator cooling. 


Turbine stage Effectiveness

 

 Case 8 First Stage pressure is 1893 psi and Turbine efficiency is 36.12%..

Effectiveness factors for each turbine stage have been determined based on the ratio of design to actual plant commissioning data. Turbine stage effectivesness remains constant whether the base or model plant conditions, they are:

HP: 0.95     IP1: 0.99    LP1: 1.0    LP2: 0.99     LP3: 1.00      LP4: 1.02            
          

Last Turbine Stage Moisture for Case 4 is calculated at 8.04%


Case 8 Results:

Mass Balance Correlation (page 5): Last State flow: 2833696/ 2859593 = 0.9909 compared to the base case of  0.9911.  Energy balance Correlation was: 1.16 compared to the base case of 0.9811, significantly higher.


Cycle Eff, %: was 33.2% identical to the coal base  The loss in unit efficiencies is not particularly significant because the objective is to burn large quantities of waste fuel rather than conserving it.


Emissions:


Researchers accidently find industrial waste, orange peel material sucks mercury out of water

6432 tons of waste were combusted for Case 8 in a 24 hour period exceeding the 5961 tons/day for the coal reference case at essentially the same rate of power generation which is precisely what is desired to rid municipalities of accumulated solid waste.

Sulfur content of Case 8 fuel is 200.66 ppm compared to 133.21 ppm.for the base case before SO2 scrubbing is performed. Mercury emissions are essentially zero compared to our coal reference.

The real benefit in burning an engineered fuel is that both operating cost and certain emissions can be reduced.($0.37 per million BTUs for Case 8 versus $0.45 per million BTUs for our reference coal) at $55.00 per ton and a calculated $36.55 per ton of Case 8 solid waste. 


Generation:




Case 8 produced 656.7 MW at 4491687 lbs/hr feedwater versus 656.8 MW at 4493358 lb/hr feedwater.   Adjusting to the same feed base 4493358 / 4491687 x 656.1 = 656.3  Error is (656.8 - 656.3)/ 656.8 *100 = 0.076%

Economics
 

Model electric revenue computations are based on $0.073 per Kilowatt hour.

Cost savings were considerable over coal alone while unit operation was comparable to coal.  Case 8 provided the following fuel savings at (0.02080 - 0.01492)/.02080 x 100 = 28.27%.  This section will contain generation data table results on alternate fuels

LATER


UPDATE 10/19/2017

The following eight municipal waste fuel blends have been tested.  They are best viewed with Notepad or Microsoft Write and are printable.

The test cases include complete plant model calculated data and are identified by carbon content as follows:

CASE '0" 100% Coal Base Reference     Case "1"  C:  0.5179    Case "2"  C:  0.5326    Case "3"  C:  0.5164 
CASE "4"  C: 0.5496      Case "5"  C: 0.5218   Case "6"  C: 0.5288    Case "7": Orig Coal base   Case "8"  C: 0.5470

 

Engineered fuel performance for the eight tests conducted are summarized in the Fuel Pellet Utility performance below. Unit operation was improved as a result of better Superheat and XS oxygen control.  SO2 and NOx reductions were not possible for Homer City Unit 3 because of higher tire blends in the engineered fuel. However the test series demonstrates that reductions in both SO2 and NOx are possible if additional fuel handling equipment is available.


Test '0' in the chart below is the 100% coal base case. Heatrate for 100% coal is much closer to the actual plant than the earlier fuel composition.  Case 8 had the Highest fuel heating value (14,019 Btu/lb) and gave the best results of the 8 fuels tested permitting the plant to use existing coal handling equipment without further modification expense. Power generating costs for case 8 were lower than all but the 48.3% tire blend of the earlier test series.

Coal and waste fuel costs are assumed constant for both Model test series.

      Notes:  Fuel Moisture content was 5% for this case.
                   Engineered fuel is essentially mercury free.