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The development of the production cost of oxymethylene ethers

as diesel additives from biomass

Adetoyese Olajire Oyedun1, Amit Kumar

*1, Dorian Oestreich

2, Ulrich

Arnold2, Jörg Sauer

2

1 Department of Mechanical Engineering, 10-263 Donadeo Innovation Centre for

Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.

2 Institute of Catalysis Research and Technology (IKFT), Karlsruhe Institute of Technology,

Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.

Abstract

Oxymethylene ethers (OMEs) are favoured as an important diesel additive because of

their ability to reduce soot loading, particulate matter (PM) emissions, and NOx emissions. While

some research has been done on the feasibility of producing OMEs from biomass, there is no

techno-economic assessment of OME production from biomass. In this study, we estimate the

unit cost to produce OMEn (n = 1-8) from three different biomass types common to western

Canada: whole tree woodchips, forest residues, and wheat straw. The techno-economic model

uses the OME production simulation results for 500 MT/day of dry biomass. The simulation

results show that 97.70, 98.86, and 99.80 MT/day of OME1-8 can be produced from whole tree

woodchips, forest residues, and wheat straw, respectively. The costs of producing OME per liter

over 20 years of production are $1.93 ± 0.15/L, $1.68 ± 0.14/L, and $1.66 ± 0.13/L, respectively,

at a 95% confidence level for whole tree woodchips, forest residues, and wheat straw biomass.

*Corresponding author: Tel.: +1-780-492-7797

E-mail: [email protected] (Amit Kumar).

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The sensitivity analysis results show that the internal rate of return, OME yield, capital cost, and

biomass delivery cost significantly influence OME unit price. The production price versus

capacity profile reveals that the optimum minimum price can be obtained at a plant capacity of

4000 MT/day of biomass; beyond this, the increase in capacity does not result in any appreciable

decrease in production price.

Keywords: Biomass; oxymethylene ethers; process model; gasification; techno-economic model;

diesel additive

1. Introduction

Diesel fuels are important to the world’s industrial economy; they are essential for

transportation and heavy-duty engines. Diesel engines are widely used due to their reliability,

cost-effectiveness, high combustion efficiency, and adaptability, but diesel engine exhaust

emissions seriously threaten the environment. The formation of soot, NOx, and particulate matter

(PM) during diesel engine combustion is a major problem1. These pollutants cause serious

environmental and health problems because they contain carcinogenic components. Other

combustion-related pollutants from diesel engines include carbon monoxide (CO), acid rain, total

hydrocarbons (THC), and photochemical smog. These pollutants have led to several countries

tightening emissions regulations and developing directives for implementation and compliance2.

The use of oxygenated compounds as diesel additives reduces soot loading, and many

oxygenated compounds have been considered as alternative fuels and diesel additives including

methanol, dimethoxymethane (DMM), dimethyl ether (DME), and oxymethylene ethers

(OMEs)3, 4. Mixing oxygenated compounds with diesel fuels reduces the particulate matter5 and

NOx emissions because the fuel burns at a lower combustion temperature when diesel is blended

with oxygenated compounds6. Many technical issues have been reported related to the use of

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DME, DMM, and methanol as diesel additives. Diesel/DMM blends require engine

modification7, 8; DMM and DME lower the fuel viscosity and can reduce diesel solubility at low

temperatures, thereby increasing the fuel vapour pressure9. OMEs with the chemical structure

CH3-O-[CH2-O-]n-CH3 have physical properties similar to diesel fuels and many advantages over

methanol and other oxygenated additives, such as high self-ignition properties, high miscibility

with diesel fuel in any concentration, no toxicity, and good material compatibility10-12.

Lautenschütz et al.13 provided a detailed review of the physico-chemical properties and fuel

characteristics of oxymethylene ethers.

Oxymethylene ethers (OMEs) of the order of n = 3-5 with oxygen contents of 42-51% are

regarded as a promising alternative fuel for diesel engines and as a diesel additive, and they can

be derived from natural gas, coal, and biomass1, 14. Unlike other oxygenated diesel fuel additives,

no engine modification is necessary when OMEs (n = 3-5) are added to diesel fuels1. Fleisch and

Sills15 reported that the addition of 20% OMEs (n= 3-8) to diesel fuel can reduce the amount of

powdery pollutants (mainly PM) and NOx during combustion by 80-90% and 50%, respectively.

The production of OMEs from biomass can provide an environmentally friendly alternative to

the depleting and GHG-intensive fossil fuel sources. The use of biomass as a biofuel has the

potential to reduce greenhouse gas emissions.

Because it is nearly carbon neutral, biomass as a renewable source of energy is favoured for

the production of liquid fuels, chemicals, power, and heat16-23. Biomass sources include whole

tree woodchips, forest residues, and agricultural residues. Canada has an abundant supply of

biomass, with an average of 145 million MT† of forest and agricultural biomass commercially

harvested annually24. Every year, about 8 m3 of wood per capita are harvested in Canada, making

† MT = Metric tonnes

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it the third highest in wood production per capita in the world after Finland and Sweden25. In

Alberta, agricultural residues are the largest concentrate of field-based residues, and wheat straw

availability has been estimated to be more than 6 million MT of dry biomass22, 23, 26.

Several studies reported the synthesis of OME from various pathways1, 10, 11, 14, 27-34, but few

have explored the production of OME starting from biomass35-38. OME production from

methane-based products has been presented by Burger et al.10 The OMEs are formed from

methylal and trioxane. The study also described the physical property model required for the

OME process design via this new gas-to-liquid technology route. The chemical equilibrium for

the production of poly (oxymethylene) dimethyl ethers has been presented by Burger et al.27 and

Schmitz et al.28 for the methylal/trioxane and formaldehyde/methanol pathways, respectively.

Their studies provide the needed synthesis information for modelling the production of OMEs

through the two pathways. The development of various catalysts for the synthesis of

polyoxymethylene dimethyl ethers has been reported by Wu et al.32 for Bronsted acid ionic

liquids with alkanesulfonic acids, Wang et al.31 for sulfonic acid-functionalized ionic liquids,

Zhao et al.29 for molecular sieves as catalyst, and Wu et al.39 for high Si/Al ratio HZSM-5

zeolite. The production of OMEs from biomass has been presented by Zhang et al.35, 36, who

described the thermodynamic analysis and optimized process conditions for the production of

OMEs via woody-biomass-derived syngas. Their work indicated that OME production from

woody-biomass is feasible via the gasification route, and their process model was validated with

experimental results. Mahbub et al.37 recently published a life cycle assessment (LCA) of OME

synthesis from biomass-derived syngas. The study presented a data-intensive LCA model

developed for the production of OMEs from two different kinds of forest biomass, whole tree

and forest residue. The results show that the whole tree pathway produces 27 g CO2eq/MJ of

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OME, whereas the forest residue pathway produces 18 g/CO2eq MJ of OME over 20 years of

plant life. The authors also compared the petro-diesel life cycle emission numbers with the LCA

of OMEs derived from forest biomass. An assessment of the production costs of OME

production from methanol was conducted by Schmitz et al.34 using a simplified method. An

OME production cost of $614.8/MT was obtained for a plant capacity of 1 million MT/y based

on a methanol price of $300/MT.

There are several techno-economic analyses of the production of diesel additives including

methanol and DME from biomass21, 40, 41. Sarkar et al.21 analyzed the cost of producing methanol

and DME from biomass via SilvaGas and RENUGAS gasification processes for a production

capacity of 2000 MT/day of dry biomass. They reported production costs of $0.23/L and

$0.31/L, respectively, for methanol and DME using the SilvaGas-based gasification process and

$0.36/L and $0.45/L, respectively, for methanol and DME using the RENUGAS-based

gasification process. They also reported that production costs for each fuel decrease rapidly as

the plant capacity increases from 200 to 3000 MT/day and 5000 MT/day dry biomass,

respectively, for the SilvaGas-based and RENUGAS-based gasification processes21. Tunå and

Hulterberg41 compared the techno-economic analyses of various woody biomass-based

transportation fuels, including methanol and DME, in terms of electricity and fuel costs. They

reported that the price of methanol and DME, in terms of electricity generation, is $93.2/MWh

and $107.2/MWh, respectively, while fuel costs for methanol and DME are $6.58/100km and

$4.98/100km, respectively41.

While the production of diesel additives like methanol and DME from biomass feedstocks

has been widely studied, the techno-economics of OME production from biomass has not been

reported. Therefore, the novelty of this study is the significant contribution to the knowledge

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through the techno-economics assessment of OME production from biomass, which, according

to the knowledge of the authors, has not been conducted before. Considering the importance of

OME as a diesel additive in relation to other oxygenated additives, industry and government

agencies will want an understanding of the economic feasibility of producing OMEs from

biomass.

The general objective of this novel study is to conduct a techno-economic analysis of

oxymethylene ether production from biomass feedstocks (whole tree woodchips, forest residues,

and wheat straw). The key specific objectives of this study are:

� To develop a techno-economic model to evaluate the cost to produce OMEn (n = 1-8) from

three feedstocks.

� To estimate the costs in $/L for the three feedstocks.

� To perform sensitivity analyses of the various cost parameters of OME production.

� To estimate the OME production price profile as plant capacity increases.

The results of this study will give insights into the economic feasibility of blending OMEs with

diesel. They will also help us understand which feedstock is most suitable and most feasible for

OME production from biomass.

2. Methodology

In order to develop the techno-economic model for OME production from biomass, we first

analyzed the mass and energy flows within the unit operations. To estimate costs, we used

region-specific delivered costs of biomass to evaluate the cost of producing OMEs. The analysis

assumes a plant capacity of 500 MT/day of dry biomass feedstock.

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2.1 Process description for OME production from biomass

A process model was developed using the ASPEN Plus process simulator42. Figure 1 is a

simplified block diagram showing the steps in OME production: biomass pyrolysis/gasification,

gas cleaning, syngas processing, methanol and formaldehyde (FA) production, and conversion of

methanol and FA to OMEs 35. Mass and energy balances for each piece of equipment used in the

unit operations are calculated.

Figure 1

The biomass gasification process is modeled based on the feedstocks’ proximate and ultimate

analyses (shown in Table 1). The processes considered in biomass gasification are drying,

pyrolysis, combustion, and char gasification. Feedstock drying is only considered for whole tree

woodchips and forest residues; in these, the moisture content was reduced from 50% and 35%

moisture mass fraction, respectively, to 15 %. (Wheat straw has low initial moisture content [see

Table 1] and does not need to be dried prior to pyrolysis). The dried biomass is pyrolyzed into

tar, gases, and char. Agricultural residues such as wheat straw contains more chlorine, potassium,

and sulphur than other biomass types and therefore can cause severe deposit formation and

subsequent active corrosion during thermochemical conversion43. To avoid this problem, the

biomass can be pyrolyzed at a low temperature prior to gasification to help release chlorine in the

form of tar associated with Cl or HCl and chlorine can be recaptured in the char and ash by

secondary reactions with available metals43. The next step is the gasification of the char from

pyrolysis into syngas using air as the gasification agent. The syngas is then cleaned and the tar

reduced through thermal cracking and steam reforming. In order to obtain a high methanol yield,

high hydrogen content in the syngas is required. To achieve this, the ratio of H2 and CO is

adjusted through the water-gas shift (WGS) reaction and the conversion rate of the WGS is

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varied to around 2:1. Methanol is then synthesized from the adjusted syngas at a conversion rate

of 99% and a reactor temperature of 300 oC for better catalyst activity. Part of the methanol is

converted to formaldehyde (FA) at a reactor temperature of 200 oC in the presence of air at a

conversion rate of 60%. OME is then produced from methanol and FA using a continuous

stirred-tank reactor (CSTR) with a volume of 1 L at a temperature of 60 oC and pressure of 1 bar.

The equilibrium parameters and reaction kinetics for the production of OME from methanol and

formaldehyde were obtained from Oestreich et al.44. The OME synthesis takes place in the

presence of homogenous catalyst Amberlyst 36. The reaction chain involved in the synthesis is

illustrated in Figure 2. The process model was validated with experimental results and the

validation process has been discussed extensively in earlier work by the authors36.

Table 1

Figure 2

The Aspen Plus simulation for the production of OME from whole tree woodchips and forest

residue biomass is shown in Figure 3. For the wheat straw scenario, there is no drying stage, and

the feed is directly supplied into the pyrolysis and combustion section of the model. The steam

produced from drying whole tree and forest residues is used in the gas cleaning section, and extra

water is required and heated for the wheat straw.

Figure 3

2.2 Biomass delivery costs

Biomass delivery cost refers to the total cost of delivering biomass from the forest or farm to

the OME plant and includes point of origin and transportation costs. The point of origin cost

varies and includes biomass field cost (royalty paid to farm owners or premium above the cost of

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fuel), nutrient replacement cost (considered only for wheat straw), road construction cost, and

silviculture cost. The transportation cost includes the costs of loading and unloading the

feedstock and transporting it from the field or forest to the OME plant. In this study, we assume

that the harvesting field is sustainable for a 20-year period in order to meet the biomass

requirement for the OME plant.

The three biomass feedstocks considered in this study are whole tree woodchips, forest

residues, and wheat straw. The whole tree biomass considered in this study includes trees from

Alberta’s boreal forests, which are characterized by spruce and mixed hardwood used mostly for

timber and pulp operations16, 45. Whole trees are cut, chipped, and trucked to the plants. The costs

involved in whole tree biomass operations are the logging road construction costs, silviculture

costs (associated with replanting), and the royalty paid to land owners16, 20, 21. Forest residue

biomass refers to the limbs and tops of trees recovered from the side of the road following

logging operations16, 26 and constitutes about 15-25% of the total forest biomass available

depending on the harvesting operation and activity16, 20, 21. Road construction and silviculture

costs are not considered since forest residues are transported on existing roads used for logging

operations. Wheat straw, available in abundance in Alberta, is harvested by the farm owner and

baled in the field before being transported to the plant23, 26. The wheat straw delivery cost

includes harvesting, bale collection, bale wrapping and storage, loading, transportation,

unloading, nutrient replacement, and market premium fees. Nutrient replacement after wheat

straw is removed from a field for bio-fuel production is a significant part of the delivery cost16.

In this study, both nutrient replacement cost (i.e., money paid to the farmers to purchase

fertilizers in order to replenish the nutrients initially taken up by the straw) and the market

premium fee paid to the farm owners as incentive are included.

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The calculated biomass delivery costs and the cost characteristics of the three feedstocks are

presented in Table 2. The overall delivery cost shown in Table 2 is for the base capacity of 500

MT/day considered in this study. Costs for higher capacities vary. The details of the biomass

delivery cost approach are discussed extensively in studies by Agbor et al. and Shahrukh et al.46,

47. The same approach was used in this study to estimate biomass delivery costs.

Table 2

2.3 Techno-economic analysis

Capital, operational, and production costs for the synthesis of OME from biomass are

estimated assuming a 20-year plant life. Aspen Icarus Process Evaluator software48 is used to

estimate costs of OME production.

2.3.1 Capital cost

Capital cost is the equipment cost and includes installation and indirect costs. Indirect costs

include construction, engineering, and contingency costs. The simulation results, including the

mass and energy balances of each piece of equipment for the optimal production of OME from

each biomass, are exported to the Icarus platform. The equipment used in the process is mapped

and sized, and costs are estimated. The project economics and the annual operating costs are

analyzed and determined based on a number of assumptions (see Table 3).

Table 3

An installation factor is required for the purchased equipment costs determined through the

Aspen Icarus Process Evaluator and accounts for the piping, electrical, and other installation

costs required. However, the installation factors calculated in Aspen Icarus are significantly

lower than those provided by Peters et al.49. Peters et al. suggested that a 3.02 overall installation

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factor is more appropriate than software-derived installation factors for solid-liquid plants. Hence

we calculated the installation cost of the equipment by multiplying the purchased equipment cost

by the installation factor suggested by Peters et al. The method used to estimate the capital cost,

as used by Peters et al.49 and Swanson et al. 50, is given in Table 4. The equipment considered are

the pyrolysis reactor, gasifiers, cyclone, syngas cleaning, filters, heaters, flash drums, gas

compressor, WGS reactor, methanol reactor, formaldehyde reactor, and OME CSTR reactor. The

total purchased equipment costs (TPEC) are estimated from Aspen Icarus, and the total installed

cost (TIC) was determined using the installation factor of 3.02. The indirect costs (IC) were then

estimated. These are engineering and supervision costs (32% of TPEC), legal and contractors’

fees (23% of TPEC), and construction expenses (34% of TPEC)49. Project contingency is

included as 20% of the direct and indirect cost, which is the sum of the TIC and the IC. A

location factor of 10% was included in the capital cost estimate16. The economic analysis does

not take into account financing, working capital, longer start-up times, or any other special

financial needs. For whole tree biomass, camping costs were included in the capital cost

estimate. It is assumed that whole tree biomass is harvested in a remote location away from

existing infrastructure and additional costs of 5% are incurred for staff camping16.

Table 4

2.3.2 Operating costs

Labour cost is calculated based on operators’ and supervisors’ salaries. Salaries (wages and

bonuses) are calculated using the 2016 Alberta wage rate in the Canadian salary calculator51.

Average salaries of $26.11/hr and $33.57/hr are specified for operators and supervisors. For a

500 MT/day plant capacity, 8 operators and 1 supervisor are considered per shift to operate the

plant and 3 shifts each day are assumed. The utility cost, which is mainly the cost of electricity

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used in the process, is calculated in the Aspen Icarus platform using the average electricity price

in Alberta, which in 2015 was $0.055/kWh52. The price of water and sand used for gasification is

$0.616/m53 and $7.46/MT54, respectively. The maintenance cost is reported as a percentage of

the capital cost, usually in the range of 2-10%, though in this study, 3% is assumed. Operating

charges are calculated at 25% of operating labour costs, and plant overhead, which consists of

the charges during production for services, facilities, payroll overhead, etc., was specified as

50% of the operating labour and maintenance costs. General and administrative (G&A) expenses

are costs incurred during production such as administrative salaries/expenses, research and

development, product distribution, and sales costs and are specified as 8% of operating costs.

2.3.1 Product costs

To determine the OME production cost, a discounted cash flow analysis was developed using

a 10% discounted cash flow internal rate of return (IRR) on investment over a 20-year plant life.

The financial values were adjusted and reported for the year 2016 with an assumed inflation rate

of 2%. The currency used is the US$ and the exchange rate in relation to the Canadian dollar is

considered here to be 0.7459 based on the Bank of Canada’s rates on March 3, 2016.

3. Results and Discussion

The results from the Aspen simulation and the techno-economic process model, along with

the OME production costs, are presented in this section. The sensitivity and uncertainty analyses

are also discussed.

3.1 Aspen simulation optimal results

The Aspen simulation optimal results for the production of OME from the three feedstocks

are presented in Figure 4. 97.70 MT/day, 98.86 MT/day, and 99.80 MT/day of OME1-8 are

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produced from 500 MT/day of whole tree woodchips, forest residues, and wheat straw,

respectively. The H2/CO ratio was adjusted to around 1.98:1 in the water-gas reactor (WGS) in

order to maximize the methanol production before the production of OME by varying the water-

gas shift reaction conversion rate. The optimal WGS conversion rates for whole tree, forest

residues, and wheat straw are 24.36%, 24.50% and 25.04%, respectively. The details of the

simulation model results and the influence of the different operating parameters on the OME

yield have been discussed in earlier work by the authors36.

Figure 4

3.2 Techno-economic analysis results

The key capital and the operating cost results for a plant capacity of 500 MT/day of biomass

feedstock are summarized in Table 5. The capital cost is highest (184.33 M $) for the whole tree

woodchips due to the additional drying requirement and the camping costs. The forest residue

capital cost (M$145.50) is slightly higher than that of wheat straw (M$134.71) due to the

additional drying requirement. Like the capital cost, annual operating costs for both whole tree

woodchips and forest residues are higher than those of wheat straw due to the utility costs

incurred during biomass drying.

Table 5

The OME production cost for whole tree woodchips, forest residues, and wheat straw are

$1.92/L, $1.67/L, and $1.65/L, respectively. The biomass delivery cost is higher for wheat straw

($79.86/dry MT) than both forest residues ($60.98/dry MT) and whole tree woodchips

($56.89/dry MT) (see Table 2). Initial moisture content plays a significant role in the OME

production cost and influences the capital cost. Another factor behind the high OME cost for all

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three feedstocks is the conversion of biomass to OME. The process model results for OME

production (see Figure 4) show that the conversion of feedstock to OME is around 19.3-20%.

The breakdown of the OME production cost in $ L-1 for the various cost parameters for the

three feedstocks is presented in Figure 5. The major cost components are capital costs, biomass

costs (sum of all the cost components involved in harvesting and delivery of biomass feedstock),

utilities, maintenance, and labour costs.

Figure 5

3.3 Effect of plant capacity on OME production cost

3.3.1 Scale factor

In this study, we varied the plant capacity from 500 to 5000 MT/day of dry biomass

feedstock and then used the ASPEN Icarus model to estimate the total capital cost for the

increased capacity. The estimated capital cost is then used to determine the scale factor. Figure 6

plots capital cost versus plant capacity for the three feedstocks as a function of the power law

exponent scale factor. The scale factor obtained for the three feedstocks ranges from 0.69 to

0.71. The estimated scale factor is in good agreement with the scale factors for similar

processes55-57. The value of the scale factor indicates that an increase in plant capacity will result

in significant savings and reduce the overall unit price of OME.

Figure 6

3.3.2 Plant capacity versus OME production cost profile

At a plant capacity of 500 t day-1 of biomass feedstock, wheat straw has the lowest OME

production cost (1.65 $ L-1) followed by forest residues (1.67 $ L-1) and whole tree woodchips

(1.92 $ L-1). Earlier studies on the production of biofuel and chemicals from biomass feedstocks

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show that the production cost decreases with capacity due to economies of scale until an

optimum capacity is reached16, 20, 45, 47, 58, 59.

The production costs of OME from different feedstocks are plotted as a function of the plant

capacity (see Figure 7). As expected, production costs decline sharply at first as the plant

capacity increases and eventually reach their lowest at 4000 MT/day of dry biomass for the three

feedstocks. The lowest OME production costs are obtained at a plant capacity of 4000 MT/day

are $0.89/L, $0.91/L, and $1.01/L for whole tree woodchips, forest residues and wheat straw,

respectively.

Figure 7

At plant capacities above 4000 MT/day (i.e., 5000 MT/day), the capital and the utility costs

increase rapidly and do not further reduce the OME price, although the biomass delivery cost

drops slightly. For a plant capacity of 4000 MT/day of dry biomass, the whole tree woodchip,

forest residue, and wheat straw biomass requirements are 0.25 million MT, 0.45 million MT, and

0.35 million MT, respectively. The availability of biomass in the province, as reported earlier by

Kumar et al.16 and Sarkar and Kumar45, shows that there is enough feedstock to operate the

facility at higher capacity. Therefore, it is better to operate the plant at a higher capacity, given

the large reduction in OME price and the biomass availability.

3.3.3 Comparison of OME production cost with literature data and similar products

An assessment of the production costs of OME production from methanol was conducted by

Schmitz et al.34 using a simplified method. They reported an OME production cost of $614.8/MT

for a plant capacity of 1 million MT/y based on a methanol price of $300/MT. When their OME

production cost is converted to $/L (assuming an average OME density of 1.032 kg/L60), the

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result is $0.634/L. While this number is lower than the number obtained in the present study

($0.89/L for whole tree woodchips at 4000 MT/day capacity), Schmitz et al. based their OME

production cost estimation on methanol from fossil sources as feedstocks. According to Schmitz

et al.34, if the methanol price increases to more than $500/MT, OME prices will subsequently

increase to about $1.00/L at the same capacity. Trippe et al.61 developed a comprehensive

techno-economic assessment for DME synthesis from biomass to produce liquid fuels. They

reported a production cost of $0.82/L in 2013. This cost is similar to the cost we reported in this

study for the production of OME.

3.3.4 Comparison of OME production cost with diesel fuel cost

In this section, the OME production cost is compared with the diesel fuel cost. The monthly

average retail price of diesel in Calgary, AB, from January-December 2014 was approximately

$0.85-1.03/L62. After deducting the federal and provincial taxes and marketing costs, we

calculated the diesel production cost to be approximately $0.62-0.81/L63.

To compare the lowest OME production cost obtained in this study with conventional diesel

costs, OME and diesel fuel production cost estimates (in $/MJ) included the heating value and

density of both fuels. The lower heating value (LHV) of diesel with a cetane number of 56.5 and

a density of 0.83 kg/L is 42.68 MJ/kg64. The average LHV values reported for OME1-6 is 19.483

MJ/kg with an average density of 1.032 kg/L60. The LHV value of diesel is equivalent to 35.42

MJ/L, while the LHV value of OME is equivalent to 20.107 MJ/L.

Therefore, the estimated OME production costs in $ MJ-1 for whole tree woodchips, forest

residues, and wheat straw are $0.0443/MJ, $0.0453/MJ, and $0.0502/MJ, respectively. These

costs are based on the results for the optimum capacity of 4000 MT/day of dry biomass. The

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estimated costs of diesel fuel range from $0.0175 – 0.0229/MJ. The lowest OME price obtained

in this study is much higher than the production cost of conventional diesel. Therefore, when

OME is blended with diesel as an additive, the OME production cost will have considerable

influence on the blended fuel cost. Further studies to improve OME synthesis in order to reduce

OME production cost are essential.

3.4 Sensitivity analysis

Key variables are selected based on their ability to change the results of the economic

analysis and the OME price. Capital and biomass delivery costs are particularly important

sensitivity variables due to the uncertainties associated with their estimation.

To determine the effects of the techno-economic parameters on the price of OME, a

sensitivity analysis for the three biomass feedstocks was conducted by varying the cost

parameters. The varied cost parameters are OME yield, capital cost, biomass delivery cost, IRR,

utility cost, labour, and maintenance costs. The IRR is varied from 8% to 20%. The capital cost

and biomass delivery cost are varied by ±30% and ±25%, respectively, based on studies by

Swanson et al.50 and Wright et al.65 on the production of liquid fuels from biomass. The

maintenance cost is also varied by ±30% since it is a function of the capital cost. The effect of

OME yield on OME production cost is determined by varying the current yield from 95% to

110%. This increase in OME yield is expected because more advanced research on the methanol-

to-OME pathway is anticipated. The utility and labour costs are varied by ±20%.

The OME production cost’s sensitivity to the cost parameters is shown in Figure 8. The most

influential cost parameter is the IRR. When the IRR is reduced from 10% to 5%, the OME

production costs drop to $1.63/L (15%), $1.44/L (14%), and $1.43/L1 (13%), respectively, for

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whole tree, forest residues, and wheat straw at a plant capacity of 500 MT/day. On the other

hand, an increase in IRR to 20% results in a 34 – 40% increase in OME production costs,

depending on the biomass feedstock.

The OME production cost is also strongly dependent upon the OME yield and process capital

costs. When the OME yield is increased by 10%, the production cost falls by 9% for all biomass

feedstocks. The OME yield, therefore, has a negative influence on the production cost for all

three feedstocks. For the lower and upper values of the capital cost (ranging from – 30% to 30%

of the baseline value), the OME production cost changes by ±9% relative to its baseline value.

The biomass delivery costs are also slightly sensitive to the production cost. A ±25% change to

the baseline value of the biomass delivery cost results in changes of ±5%, ±4%, and ±3% in the

OME production cost for wheat straw, forest residues, and whole tree, respectively. The higher

percentage for wheat straw is due to its high delivery cost.

Other parameters, including maintenance cost and labour cost, have little impact on the

production cost.

Figure 8

3.5 Uncertainty analysis

The sensitivity analysis discussed in the previous section provides only single point

deterministic estimates for the OME production cost. The analysis also reflects the effects on the

production cost of a single parameter at a time. The lack of precise field data could bring

inherent uncertainties in the cost estimates. In most cases, appropriate data sources and

assumptions are used. However, uncertainty in the systems needs to be considered. To address

the uncertainty, a Monte Carlo simulation is used as proposed by Raynolds et al.66.

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In this study, a Monte Carlo simulation was conducted using the economic parameters that

most influenced production cost. ModelRisk software67 was used to perform 100,000 iterations

in order to obtain accurate results. A triangular probability distribution was adopted in this study

as it is commonly adopted in both published and estimated data. The uncertainty in the system is

estimated by identifying the significant cost parameters through sensitivity analyses and then

assigning a suitable uncertainty to each parameter based on the information available.

The Monte Carlo simulation results for the OME production costs for the three feedstocks at

a plant capacity of 500 MT/day are depicted in Figure 9. The results show that the 95%

probability range for the OME production costs is $1.87 – 2.08/L (-5% to +16% relative to the

estimated cost, $1.92/L) for whole tree woodchips, $1.62 – 1.81/L (-5% to +14% relative to the

estimated cost, $1.67/L) for forest residues, and $1.60 – 1.79/L (-5% to +14% relative to the

estimated cost, $1.65/L) for wheat straw.

The uncertainty analysis results show that with the assumed uncertainties in the selected cost

parameters, the production cost of OME tends to be higher than the estimated value by about 14

– 16%. The uncertainty results for the OME production costs in terms of mean and standard

deviation for whole tree, forest residues, and wheat straw are $1.970 ± 0.191/L, $1.710 ±

0.173/L, and $1.689 ± 0.167/L, respectively, at a 95% confidence level.

Figure 9

4. Conclusion

In this study, a techno-economic model was developed to estimate the cost of producing

oxymethylene ethers (OMEn) of the order n = 1 – 8 from three biomass feedstocks, whole tree

woodchips, forest residues, and wheat straw. The techno-economic model used the Aspen Plus

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simulation optimal design model results to simulate the production of OME from 500 MT/day of

dry biomass feedstock. The optimal design results show that 97.70, 96.33, and 99.80 MT/day of

OME1-8 can be produced from whole tree woodchips, forest residues, and wheat straw,

respectively. The OME production costs estimated at zero NPV for 20 years of production

including uncertainty are $1.970 ± 0.191/L, $1.710 ± 0.173/L, and $1.689 ± 0.167/L, for whole

tree woodchips, forest residues, and wheat straw biomass, respectively, at a 95% confidence

level. Wheat straw has the lowest OME production cost due to the low initial moisture content

compared to the other two feedstocks. The minimum OME production cost as plant capacity

increases is obtained at 4000 MT/day of dry biomass for all three feedstocks. At this capacity,

whole tree woodchips have the lowest OME production cost ($0.89/L) followed by forest

residues ($0.91/L) and wheat straw ($1.01/L).

The sensitivity analysis of key process variables found IRR, OME yield and capital cost to

have significant influence on OME production cost. Other cost parameters, such as biomass

delivery cost and utility costs, also have appreciable impact on OME production cost.

Maintenance cost and labour cost have limited impact on the OME production cost. The degree

of the sensitivity of each variable largely depends on the biomass feedstock type.

This study gives more insights on the economic and technological feasibility of producing

OME from biomass for the purpose of blending OMEs with diesel. While we have considered

OMEs 1-8 in this study, further studies can focus on the separation of OME to optimize the

production of OMEs 3-5, which can be readily used in diesel engines without engine

modification.

Acknowledgements

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The authors are grateful to the Helmholtz-Alberta Initiative (HAI) (Grant number:

AE10GREA18) and the University of Alberta for the financial support for this work. Astrid

Blodgett is thanked for editorial assistance.

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Figures

Figure 1: Simplified unit operations for OME production from biomass gasification.

Raw BiomassDrier Gasifier

Pyrolysis

Gasification

Combustion

Gas cleaningTar cracking

Tar reforming

Cyclone

Syngas cooling

Dust filtering

Syngas processingWater gas shift reaction

CO2 removing

MeOH and FA

productionMethanol

Formaldehyde

OME

SynthesisOMEs

OMEn (n = 1-8)

Air/O2/

Steam/CO2 Steam/O2 Catalyst Air Catalyst Catalyst

CO2

Glycols,

Hemi-formals/hemiacetals

MeOH, CH2O

H2O

Sand

Sand H2O

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Figure 2: Reactions for the production of OMEs from methanol and formaldehyde (FA: formaldehyde, Gly: glycols, Tri: trioxane, HF: hemi-formals/hemiacetals, OME: oxymethylene ethers, MeOH: methanol).

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Figure 3: Aspen Plus model for the production of OMEs from whole tree and forest residue biomass.

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(a) – Whole tree woodchips

(b) – Forest residues

(c) – Wheat straw

Figure 4: Process model optimal results for OME production from (a) whole tree woodchips, (b)

forest residues and (c) wheat straw.

Gasification

Whole tree woodchips:500 MT/day

Raw Syngas(mol/s)

H2: 38.43CO: 45.31CO2: 86.23H2O: 77.45N2: 271.58O2: 25.44CH4: 2.19Others: 12.55

H2/CO: 0.85:1

GasCleaningand

Adjusting

Cleaned Syngas(mol/s)


H2/CO: 1.98:1

MethanolSynthesis

FormaldehydeSynthesis

OMEsSynthesis

Mass flow(MT/day)

OME1: 38.30

OME2: 25.28

OME3: 15.36

OME4: 8.87

OME5: 4.96

OME6: 2.71

OME7: 1.45

OME8: 0.77

Total: 97.70

Air:329.11 MT/day

Methanol

255.84 MT/day

Gasification

Forest Residue:500 MT/day

Raw Syngas(mol/s)

H2: 44.36

CO: 49.09CO2: 70.03H2O: 70.05

N2: 208.69O2: 23.72CH4: 2.034Others: 12.17

H2/CO: 0.90:1

GasCleaningand

Adjusting

Cleaned Syngas(mol/s)

H2: 192.88

CO: 97.89CO2: 102.61H2O: 0.77N2: 208.69

O2: 23.72CH4: 0.46Others: 0.51

H2/CO: 1.98:1

MethanolSynthesis

FormaldehydeSynthesis

OMEsSynthesis

Mass flow(MT/day)

OME1: 38.75

OME2: 25.59

OME3: 15.54

OME4: 8.98

OME5: 5.02

OME6: 1.47

OME7: 1.47

OME8: 0.78

Total: 98.86

Air:330.50 MT/day

Methanol

257.26 MT/day

Gasification

Wheat straw:500 MT/day

Raw Syngas(mol/s)

H2: 45.89CO: 50.13CO2: 57.42H2O: 65.66N2: 150.69 O2: 24.66CH4: 2.12Others: 12.90

H2/CO: 0.92:1

GasCleaningand

Adjusting

CleanedSyngas(mol/s)


H2/CO: 1.98:1

MethanolSynthesis

FormaldehydeSynthesis OMEs

Synthesis

Mass flow(MT/day)

OME1: 39.12

OME2: 25.83

OME3: 15.69

OME4: 9.06

OME5: 5.07

OME6: 2.77

OME7: 1.48

OME8: 0.78

Total: 99.80

Air:336.13 MT/day

Methanol

261.30 MT/day

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Figure 5: Breakdown of OME production costs ($/L) for the different cost parameters.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

OME - Wheat straw OME - Forest residue OME - Woodchips

Production cost of OMEs, $/L

Biomass feedstock

General &administrative cost

Operating charges

Maintenance cost

Labour cost

Plant overhead

Utility cost

Feedstock cost

Capital cost

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Figure 6: Capital costs at different plant capacities for the three feedstocks.

Figure 7: OME production costs at different plant capacities for the three feedstocks.

y = 1.6467x0.713

R² = 0.991

y = 1.9431x0.705

R² = 0.9876

y = 2.4982x0.6903

R² = 0.9937

0

100

200

300

400

500

600

700

800

900

1000

0 1000 2000 3000 4000 5000

Total Capital costs, M

$

Production capacity, MT/day

Wheat straw

Forest residue

Whole tree woodchips

Power (Wheat straw)

Power (Forest residue)

Power (Whole tree woodchips)

0.8

1

1.2

1.4

1.6

1.8

2

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

OME production cost, $/L

Production capacity, MT/day

Wheat straw

Forest residue

Whole tree woodchips

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1.59 1.79 1.99 2.19 2.39 2.59

Labour (80: 100: 120%)

Maintenance cost (70: 100: 130%)

Biomass delivery cost (75: 100: 125%)

Utilities (80: 100: 120%)

OME Yield (110: 100: 95%)

Capital Cost (70: 100: 130%)

IRR (5: 10: 20%)


Favorable

Unfavorable

1.43 1.53 1.63 1.73 1.83 1.93 2.03 2.13 2.23 2.33

Labour (80: 100: 120%)



Utilities (80: 100: 120%)

Capital Cost (70: 100: 130%)

OME Yield (110: 100: 95%)

IRR (5: 10: 20%)


Favorable

Unfavorable

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(c) – Wheat straw

Figure 8: Sensitivity analysis results on OME production costs for (a) whole tree woodchips, (b)

forest residues, and (c) wheat straw, in the order of favorable, baseline and unfavorable.

1.43 1.53 1.63 1.73 1.83 1.93 2.03 2.13 2.23

Labour (80: 100: 120%)


Utilities (80: 100: 120%)


Capital Cost (70: 100: 130%)

OME Yield (110: 100: 95%)

IRR (5: 10: 20%)


Favorable

Unfavorable

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(c) – Wheat straw

Figure 9: Uncertainty analysis results on OME production costs for (a) whole tree woodchips, (b)

forest residues, and (c) wheat straw.

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Tables

Table 1: Proximate and ultimate analyses of the biomass feedstocks studied

Parameters Whole tree woodchips Forest residue Wheat straw

Initial moisture mass fraction (%) 50 35 15

Proximate analysis a (%)

Fixed carbon 15.96 15.30 16.34

Volatile matter 82.37 81.28 74.13

Ash 1.660 3.430 9.530

Ultimate analysis a, (%)

C 48.25 46.97 42.41

H 6.190 5.980 5.730

N 0.140 0.120 0.870

S 0.002 0.003 0.010

Ob 45.42 46.87 50.56

Cl 0.054 0.053 0.416

a Calculated on dry basis, i.e., actual wet yields are adjusted to zero moisture mass fraction. b Calculated by difference.

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Table 2: Biomass delivery cost characteristics

Items Values Formulas, Sources and

Comments

Whole tree (woodchips)

Biomass yield (MT/ha) 92.11 Assumed based on hardwood

yield in Alberta16,45. Dry basis a.

Royalty/premium fee ($/MT) 6.97 Royalty paid to farmers16,45. Dry

basis a.

Harvesting cost:

16,45-47. Dry basis a.

Felling ($/MT) 11.94

Skidding ($/MT) 10.13

Chipping cost ($/MT) 10.28

Log loading, unloading, and transport cost

($/MT)

15.15 2.91+0.0326D

A circular harvesting area is

assumed where D = 2*Average

radius required to collect the

biomass feedstock and

represents the round-trip road

distance from the forest to the

receiving plant [17, 38-40]. Dry

basis a.

Road construction and infrastructure costs

($/MT)

0.07 [1.27 + (635.5/VT)] *Average

gross yield16,45-47. Dry basis a.

Silviculture cost ($/ha) 2.35 16,45-47

Whole tree delivery cost ($/MT) 56.89b

Forest residue

Biomass yield (MT/ha) 0.247 16,20-21,46-47. Dry basis a.

Royalty/premium fee ($/MT) 6.97 Fee paid to farmers.

16,20-21,46-47. Dry basis a.

Harvesting cost ($/MT) 16.74

Chipping cost ($/MT) 16.42

Loading, unloading, and transport cost 20.84 2.91+0.0326D16,20-21,46-47. Dry

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($/MT) basis a.

Forest residue delivery cost ($/MT) 60.98b

Wheat straw

Biomass yield (MT/ha) 0.38 16,20. Dry basis a.

Royalty/premium fee ($/MT) 6.97 Fee paid to farmers. Dry basis a.

Harvesting cost:

23. Dry basis a.

Shredding ($/MT) 4.30

Raking ($/MT) 2.71

Baling ($/MT) 4.28

Bale wrapping-twine ($/MT) 0.57

Bale collection:

Bale picker ($/MT) 0.79 23. Dry basis a.

Tractor ($/MT) 4.19

Bale storage:

On-field storage ($/MT) 2.11 23. Dry basis a.

Storage premium ($/MT) 0.12

Loading, unloading, & transport cost ($/MT) 27.60 6.7+0.1843D23. Dry basis a.

Nutrient replacement cost ($/MT) 26.23 23. Dry basis a.

Straw delivery cost ($/MT) 79.86b

a For all biomass, the reported yields or weights are on a dry weight basis, i.e., actual wet yields are adjusted to zero moisture mass fraction. Estimated actual moisture mass fraction is 50% for whole tree woodchips. 35% for forest residues, and 15% for wheat straw. b. All the delivery cost numbers are for a plant capacity of 500 MT/day.

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Table 3: Assumptions for economic evaluation

Parameters Value Sources

Plant life (years) 20 Assumed

Operation season (hours) 8000 Assumed

Annual IRR 10% Assumed

Depreciation method Straight line

Aspen Icarus48.

Project capital and product

escalation

5%

Raw material escalation 3.5%

Operating cost, labour, utilities,

and maintenance escalation

3%

Capital cost spread Taken from earlier studies

16,45-47 Year 1 20%

Year 2 35%

Year 3 45%

Production capacity factor Taken from earlier studies

16,45-47 Year 1 0.7

Year 2 0.8

Year 3 and onward 0.85

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Table 4: Method used to estimate capital cost49

Parameters Method

Total purchased equipment cost (TPEC) Aspen Icarus Process Evaluator

Total installed cost (TIC) TPEC installation factor

Indirect cost (IC) 89% of TPEC

Total direct and indirect costs (TDIC) TIC + IC

Contingency 20% of TDIC

Fixed capital investment (FCI) TDIC + contingency

Location factor (LF) 10% of FCI

Total capital cost FCI + LF

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