Biofuels, Solar and Wind as Renewable Energy Systems_Benefits and Risks Episode 2 Part 1 pot

10.2.2.1 Biomass Yield Parameters For a given BFC: Ncrop to bfp= YcropA YbfpHere Ncrop to bfp is the BFC net fuel production, Ycrop is the agriculture stagebiomass crop yield, A is the p

The second parameter type is the individual parameters (pk’s and⌬k’s discussed inSection 10.2.2.2) unique to a given module Sub-activity In the BFCM treatment,

Ycropand Ybfpvariability relationships are examined separately from the pkvalues

10.2.2.1 Biomass Yield Parameters

For a given BFC:

Ncrop to bfp= YcropA YbfpHere Ncrop to bfp is the BFC net fuel production, Ycrop is the agriculture stagebiomass crop yield, A is the planted land area, and Ybfp is the biofuel productionstage yield Another BFC general yield and biofuel energy relationship is:

Ebiofuel= Ncorn to bfpUEfuel eHere Ebiofuelis the BFC created biofuel energy and UEfuel eis the biofuel useableenergy (see Section 10.3) Combining and rearranging these two equations:

Ebiofuel/A = YcropYbfpUEbiofuel (10.1)Ebiofuel/A is a measure of the BFC crop and biomass fuel production effi-ciency in creating the biofuel This equation enables biofuel yield evaluation (seeSection 10.4.1) at both the local/regional and national fuel cycle production lev-els Clearly gains in crop and process yields mean higher biofuel energy per acreplanted

10.2.2.2 Template Parameters

For each template Activity, there is an assigned k value This k value is used to indexthe pkvalue assigned to that Activity and it’s associated Sub-activities The pkvalueand it’s uncertainty⌬kare specific numerical values used in the analysis Consider,for example, in Template 1 (Table 10.1) under the Facilities Phase there is the SeedPlant Sub-phase It’s assigned Activity and associated Sub-activities index value is

k = 5 Therefore it’s numerical values used in an analysis are assigned to the p5and⌬5 parameter in the BFCM equations discussed here (see also Section 10.4.2for specific illustration) The pk’s are used to calculate the Smodule jvalue of interest:

Smodule j= fj(pk)and the⌬k’s are used to quantify the uncertainty (⌬j) associated with that Smodule j(see Section 10.2.4) The fj(pk) equations are typically simple summations for theBFC’s but can be any mathematical relationship The detail for a given Smodule jisdetermined by the BFC scenario and associated module Both the Smodule jvalue andits’⌬ are used to quantifying and characterizing the BFC

The general relationship applicable to each module is:

mod-BFC yields, pk’s, and⌬k’s values, which are annual numbers, are reported in ous units in the literature In order to sum the Smodule j‘s, the data must be normalize

vari-to a common unit In the current treatment the numerical values are normalized

to Btu/Acre The conversion factors used were: 948.452 Btu/MJ, 0.2520 Kcal/Btu,3.7854 L/Gal, and 2.471 Acre/Ha The Biorefinery pk values were normalized toBtu/Acre using each specific study crop and biofuel yields The resultant Smodule 3values are thus a function of these specific yields which introduces two sources ofvariability into the analysis

10.2.3 BFC Boundaries

A fundamental consideration is the establishment of the given BFC boundaries As

is evident from the results shown in Fig 10.1, the choice of boundaries can matically change results It is important to clearly and concisely disposition what isincluded in and excluded from the BFC

dra-The boundaries for a given BFC are established by using Templates 1, 2, and 3(see Tables 10.1, 10.2, and 10.3 respectively) as the starting point The three tem-plates cover a broader range of BFC aspects than typically addressed Their level

of Sub-activity breakout focuses on aspects needing explicate dispositioning TheSub-activities encompass materials, components, and facilities starting from naturalresources through fabrication and usage to disposal The pk’s quantify aspects such

as raw material extraction (e.g., mining of coal and minerals, petroleum drilling),materials fabrication (e.g., steel, fuel, fertilizer, farm equipment), construction (e.g.,facilities, roads), operation (e.g., farming, storage, processing, transporting), andwaste management (e.g., discharges, emissions, equipment and facility replaced ordecommissioned)

The dispositioning (i.e., inclusion or exclusion) of a pkis a boundary decision.The BFC modules enable capturing the justification, including quantification of theimpact, of Sub-activity exclusion However, as evidenced in Fig 10.1, Sub-activityexclusion can result in important differences between models Inclusion has the ad-vantages of simplifying the description, facilitating cross model comparison andevaluation, and minimizing the potential for underestimating (which is inherent toBFC’s as a result of their cumulative parameter property)

The energy definitions given in Section 10.3 establish the BFC energy boundariesand accounting of fuel use Considerations of financial, subsidy, policy, economic,and national security based aspects of a fuel cycle may provide insight into fuelcycle boundaries but should not be used as a basis for disposition because of theirintroduction of bias.

The end result is the BFC Stage Sub-activities and boundary demarcations areclearly delineated and justified And the pkand⌬kvalues are presented in a standardformat

10.2.4 Statistical Tools

Use of statistical tools in the BFCM is intended to facilitate error reduction Sources

of imprecision and uncertainty arise from non-random (determinate) and random(indeterminate) errors resulting from method, measurement, estimation, and/ormodel decisions Non-random errors can be difficult to detect Consistent appli-cation of the BFCM approach provides one tool of use in avoiding and detectingerrors

The following statistical tools can be used to reduce random error, evaluate pkand

⌬ksignificance, identify pk’s and⌬k’s whose refinement will improve Smodule jacterization, assessing boundary dispositions, and minimize introduction of bias.The present study assumes the following normal distribution relationships apply(Natrella, 1966; NIST, 2006; Skoog and West, 1963):

␴ = standard deviation =

n

i =1(xi− m)2 /(n − 1)

One can treat the square of the uncertainty (⌬2

i) associated with each numericalvalue in a given equation as a variance equivalent and apply absolute and relativedeviation addition methods (Skoog and West, 1963) to obtain⌬k‘s and⌬j‘s As anexample, for the general relationship:

⌬ = fj(⌬k)

the method first treats sums or differences (±) using

1/2

as one proceeds from the interior of the function outward Here n is the number ofuncertainty values associated with the numerical values in the fj(⌬k) equation.

10.3 BFC Fuel and Net Energy Balance Definitions

The BFC energy measure of interest is the Net Energy Balance (NEB):

NEB= Total BFC Energy Gain (EG) – Total BFC Energy Loss (EL)

= TEG − TEL Concise definition of EG and EL facilitates BFCM ary dispositioning, energy accounting, and consistency

bound-10.3.1 Fuel Energy Definitions

When calculating the NEB, the energy gain (i.e., creation of fuel or productiveuse of BFC biomass or biofuel) and loss (i.e., consumption/expending of non-BFCfuel or energy) accounting needs to be well defined The energy independence andenvironmental national goals lead to replacement of fossil fuels (both foreign anddomestic) with domestic biomass fuels BFC energy accounting needs to addressall energy consumptions The BFC energy definitions that follow directly from theabove considerations are:

EL = Energy Loss for given BFC = directly (e.g., burned at given BFC cility) or indirectly (e.g., resource extraction/production/refinement, electric-ity generation, steam generation, transport) expended fossil (i.e., petroleum,coal) fuels, biomass/biofuel, electricity, or energy (e.g., heat) via nuclear/solar/water/wind power

fa-EG = Energy Gain for given BFC = created biofuels productive combustion(e.g., ethanol fuel oxidant in gasoline, ethanol replacement of gasoline,biodiesel replacement of petroleum diesel)+ biomass or BFC created co-products combustion supplying productive heat and/or power (e.g., silage,bagasse) + biomass, biofuels, or coproduct conversion to products (e.g.,

biomass digestion resulting in fertilizers, silage composting resulting inlowered field fertilization, conversion of biofuel to pesticides) that dis-place corresponding products derived from fossil (i.e., petroleum, coal)fuel.

Note both EL and EG include biomass/biofuel used to supply energy to the givenBFC The inclusion in both is needed in order to have the actual total energy valuetabulated for the TEL and TEG In this way both the TEL and TEG values arecomprehensive and unencumbered with BFC specific exceptions/treatments Theaccounting of the gain resulting from consumed biomass/biofuel displacing fossilfuel is captured in the EG analysis (see Section 10.3.3)

These definitions provide the basis for: excluding through definition the solarenergy absorbed in growing the biomass and the caloric energy expended by BFClabor; retention of coproduct energy within the cycle unless some portion of theenergy expended to create the coproduct is productively recovered by combustion ofthe coproduct; treating the use of solid, liquid, or gaseous biomass or biofuel within

a given BFC as equivalent to an energy gain (i.e., those biomass fuel consumptionsavoid consuming fossil fuels); and treating cogeneration as equivalent to an energygain (i.e., it avoids consuming fossil fuels) The labor and coproduct aspects arediscussed further in Section 10.5

10.3.2 Fuel Useable Energy

The combustion of a fuel can be simplistically viewed as resulting in energy eration, water (as a gas) containing energy in the form of steam heat, combustionproducts, and particulates For fossil, biomass, and biofuel fuels, the relevant energyvalue is the usable energy realized when a quantity of fuel is burned under normaluse conditions:

gen-UE= Useable Energy = fuel High Heat Value (HHV) adjusted for normal uselosses (L) HHV is also referred to as the gross heat content of a fuel Combustionsystems differ in their L value due to inefficiencies (e.g., heat leaks, energy transfer,discharge, friction) and operational variations

For internal combustion engines it is typically assumed the efficiency is the samefor all liquid fuels and the main loss is via steam This L adjusted HHV is commonlyreferred to as the Low Heat Value (LHV) for the fuel (also called the net heat con-tent) and is commonly used as the UE value Use of the LHV provides a consistent,common base of comparison Productive use of L, such as preheater use of boilersystem exhaust, increases the UE value with respect to the LHV

For combustion of solid fuels (e.g., crop biomass such as bagasse), the aboveassumptions and conditions are not applicable The L value is much more fuel com-position and system efficiency dependent Capturing BFC energy credit for the use

of biomass fuel in place of fossil fuel (e.g., co-generation, pre-heating a processstream) requires consideration of system application specifics

10.3.3 Fuel Energy Templates and Analysis

When performing the energy EL, EG, and NEB analyses, four templates are used.The Section 10.2.1 Templates 1, 2, and 3 are used to create the BFC specific ELModules which are then used for the TEL tabulations The Template 4 given inTable 10.4 is used to create the BFC specific EG Module for the TEG tabulation Inall energy Module tabulations, the applicable UE value should be used

Table 10.4 Template 4 Energy Gain Stage (j= 4)

External-to-Given BFC Combustion of BFC Created Fuels: Biofuel, Biomass

Combustion of Biomass or coproducts for Heat and/or Power Fossil feedstock based products Displacement by Biomass, Biofuel, or coproduct

Infrastructure Manufacture Operations Fuels: Biofuel, Biomass

Facilities Operations Fuels: Biofuel, Biomass Agriculture Operations Fuels: Biofuel, Biomass

Biofuel Production Biorefinery Plant Operations Fuels: Biofuel, Biomass

Fuel Handling Facility Operation Fuels: Biofuel, Biomass

Applying the equation 10.2 relationship to the Modules, where we hold U stant, define Smodule j= Emodule j, and calculate the EL’s and EG’s on a per unit areabasis, gives the general BFCM equations:

con-TELBFC=

q



j =1Emodule j

10.4.1 Analyzing Yield Aspects

The two main BFC liquid biofuels products are ethanol (e) and biodiesel (d) sider the created ethanol fuel energy per acre for the corn to ethanol BFC where theportion F of corn processed through the wet versus dry milling is varied Based onequation 10.1 the energy-yield relationship is:

Con-Ee/A (Btu/Acre) = YC[YDF+ YW(1− F)]Ebiofuel e

Here YDis the Ybfpfor corn to ethanol Dry mill processing, YWis the Ybfpfor corn

to ethanol Wet mill processing, F is the fraction of ethanol corn Dry mill processed,and Ebiofuel eis the ethanol UE fuel value Figure 10.2 shows the Ee/A linear leastsquare fit results for some corn and ethanol production yields

From a local/regional and national perspective, the potential gain from BFCimprovement is an important consideration The equation 10.1 Ee/A yield relation-ship provides insight into such considerations Large variations in corn yields oc-cur as the result of soil, weather, and crop management practices: 85–245 Bu/Acre(Dobermann and Shapiro, 2004) For biorefinery yields in the 2.6 Gal/Bu range, aregion producing at 140 Bu/Acre will attain Ee/A values 25% higher than a region

E e / A as a Function of Mill Mix and Mill Yield

Ebiofuel e = 7.57E+4 Btu/Gal

Fig 10.2 BFC created ethanol fuel energy per acre as a function of crop yields and corn to ethanol

mill processing yields

producing 112 Bu/Acre Alternatively, processing the 112 Bu/Acre region corn at

a 2.8 Gal/Bu biorefinery achieves 8% higher Ee/A value over the 2.6 Gal/Bu ity A subset of this is Wet versus Dry mill utilization considerations illustrated inFigure 10.2 The BFCM facilitates such local/regional YCand Ybfpcoupled evalua-tions which may be of value to National energy considerations

facil-For the soybean to biodiesel BFC the created biodiesel energy per acre is:

Ed/A (Btu/Acre) = YSYdEbiofuel dCombining the corn and soybean crop rotation and fuel production BFC’s:

Eed/A (Btu/Acre) = YCCR [YDF+ YW(1− F)] Efuel e+ YS(1− CR) YdEfuel dHere Eed/A is the combined energy content of ethanol and biodiesel fuel producedand CR is the crop rotation cycle fraction for corn planting (e.g., alternating plant-ings: CR = 0.5; 2 out of every 3 plantings: CR = 0.67) Figure 10.3 showssome of the possible correlation plots For current yield conditions, annual croprotation gives an Eed/A of 1.73 × 10 +7Btu/Acre while corn only (i.e., no rotation)gives 5.50 × 10+7Btu/Acre for the comparable 2 year period Examination of theleft (100% soybean) and right (100% corn) axes shows optimization of the corn

to ethanol parameters holds the greater promise for improving biofuel productionefficiency, despite Ebiofuel dbeing 1.55 times Ebiofuel e However, this result does notaddress the NEB aspects (Section 10.4.2) Nor does it factor in the need for conser-vation measures to deal with such aspects as soil depletion, crop diseases, and croppests

The CR needed to achieve an equal energy gain from each crop in the soybean BFC is given by the relationship:

corn-CR= YSYdEfuel d/[YCYMillEfuel e+ YSYdEfuel d]

Here [YDP+YW(1−P)] is defined as the corn to ethanol effective processing yieldYMill To achieve parity under the ‘current yields’ (Fig 10.3) requires a 5 plantingscrop rotation sequence comprised of 1 corn planting for every 4 soybean plantings.The alternate year crop rotation sequence approaches parity for the low corn andhigh soybean yields Again the analysis does not include NEB aspects

10.4.2 BFC Energy Scenario Models and Analysis

The structure of the energy relationships follows directly from the associated ular configuration of the BFC scenario Templates 1, 2, and 3 (Section 10.2.1) wereused to construct the Modules 1 – 9 EL tabulations given in Tables 10.5–10.13.Template 4 (Section 10.3.3) was used to construct the EG Modules 100–102given in Tables 10.14–10.16 Each Module lists the Sub-activity k assignment (see

mod-E ed /A as a Function of Corn-Soybean Crop Rotation

Ebiofuel e= 7.57E + 4 Btu/Gal

Ebiofuel d= 1.17E + 5 Btu/Gal

Fig 10.3 BFC created ethanol-biodiesel fuel energy per acre as a function of yields and crop

rotation

Section 10.2.2.2) and the number of literature data points used to obtain pk, alongwith the available⌬kvalues

Based on Section 10.3.3, the NEB equation is:

NEBBFC= TEGBFC− TELBFC=

1



i =1EGi−

q



i =1ELi

The l and q values are established by the modeled scenario Table 10.17 lists theBFC module Emodule jrelationships which were used to obtain the Table 10.18 BFCscenarios

Table 10.5 Module 1 Infrastructure for Corn energy loss EL data (EBAMM, 2007) in Btu/Acre

(j = 1)

Phase Sub-phase Activity Sub-activity k∗ n a∗pk∗ ⌬k∗

Tractors, Combines, Trucks, Manufacture Equipment Fabricate Implements 1 3 1.36 × 10+6 1.13 × 10+6

Irrigation, Treatment (water, waste) Facilities Seed Plant Physical

Plant

Operations/

fuel

5 2 4.66 × 10+5 3.89 × 10+5 Fertilizer

Plant

Physical Plant

Operations/

fuel

6 23 3.69 × 10+6 3.43 × 10+5 Herbicide

Plant

Physical Plant

Operations/

fuel

7 7 4.07 × 10+5 2.63 × 10+5 Insecticide

Plant

Physical Plant

Operations/

fuel

8 7 1.09 × 10+5 1.55 × 10+5 Lime

Facility

Physical Plant

Operations/

fuel

9 5 2.13 × 10+5 1.80 × 10+5 Biorefinery Physical

Plant

Construct 10 1 1.65 × 10+5 nvOffsite Water

Treatment

Plant

Treatment of:

Water or Wastewater

Smodule j= fj(pk)

we have for Module 1:

Smodule j= Emodule 1= f1(pk)≡ ELICwhere the f1(pk) is a summation of 8 pkterms (t= 8):

ELIC= f1(pk)=

8



t =1pk,t

Table 10.6 Module 2 Corn Agriculture energy loss EL data (EBAMM, 2007) in Btu/Acre (j= 2) Phase Sub-phase Activity Sub-activity k∗ n a∗ p∗k ⌬ ∗

Herbicide 1 Insecticide 1 Irrigation

system &

water

Operations/fuel 1 3 2.20 × 10+5 2.60 × 10+5 Pre-planting 1 In Tilling value

Planting Tilling 1 33 3.03 × 10+6 9.42 × 10+5 Field Fertilizer 1 In Tilling value

Herbicide 1 Insecticide 1 Harvest Crop and

Silage Processing

Operations/fuel 2 In Tilling value Transport:

Storage, Biorefinery

Operations/fuel 3 In Tilling value

TELCe=

3



i =1ELj= ELIC+ ELC+ ELCe= 3.025 × 10+7Btu/Acre

Table 10.7 Module 3 Corn to ethanol Production EL data (EBAMM, 2007) in Btu/Acre (j= 3) Phase Sub-

phase

Activity Sub-activity K∗ n a∗ pk∗ ⌬k∗ Biorefinery

Plant

Production Processing

to 99.5%

Ethanol

Operations/fuel 1 12 1.64 × 10+7 2.63 × 10+6 Transport of

chemicals to Plant

1 1 1.82 × 10+6 nv

Process water treatment

Table 10.8 Module 4 Infrastructure for Soybean energy loss EL data (Pimentel & Patzek, 2005)

in Btu/Acre (j = 1)

Phase Sub-phase Activity Sub-activity k∗ n∗ p∗k ⌬ ∗

k

Tractors, Combines, Trucks, Implements Manufacture Equipment Fabricate 1 1 5.78 × 10+5 nv

Irrigation, Treatment (water, waste) Facilities Seed Plant Physical

Plant

Operations/fuel 5 1 8.90 × 10+5 nvFertilizer

Plant

Physical Plant

Operations/fuel 6 3 4.22 × 10+5 nvHerbicide

Plant

Physical Plant

Operations/fuel 7 1 2.09 × 10+5 nvLime

Facility

Physical Plant

Operations/fuel 9 1 2.17 × 10+6 nvBiorefinery Physical