The feasibility analysis will be conducted in terms of both technical and economic analysis.
2.1 Model validation and results
2.1.1 Gasification
The bio-syngas composition produced from biomass gasification, carbon conversion efficiency and gasification efficiency are presented in Table 2. The simulation model and the gasifier efficiency are validated by experimental data based on biomass gasification process. The bio-syngas composition obtained through Aspen simulations is matched well with the experimental results. It is important to note that only one parameter seems to contrast with the empirical results, here the density of CH4. This difference could be explained by the fact that the steam methane reforming, at the beginning of gasification with low temperature, is restricted by temperature effect. Thus, during the experimental process the gasifier temperature rises from low temperature, during which a large amount of CH4 is produced, which is not the case in the simulation [24]. The carbon conversion efficiency of the simulation results is very close to the actual experimental process, reaching 96.1%. The gasification exergy efficiency (47.3%) obtained from the simulation is also within the exergy efficiency values of the actual gasification. This not only validates the accuracy of the simulation, but also gives an accurate indication of the total energy consumption during the gasification process.
Table 2. Comparison of experimental and simulated bio-syngas composition
Composition
|
Model result (vol. %)
|
Experiment results (vol. %) [25]
|
H2
|
57.1
|
45~55
|
CO
|
24.8
|
21~25
|
CO2
|
17.8
|
18~22
|
CH4
|
0.3
|
2~4
|
NH3
|
trace
|
-
|
H2S
|
trace
|
-
|
tar
|
trace
|
-
|
Carbon conversion efficiency (%)
|
96.1
|
87~98 [26]
|
Lower heating value (MJ/Nm3)
|
10.5
|
-
|
Gasifier efficiency (%) (based on bio-syngas LHV)
|
55.3
|
50 [27]
|
*Exergy efficiency (%)
|
47.3
|
45~50 [28]
|
*Exergy efficiency is a measure of the thermal efficiency of the actual system compared to an idealized or reversible heat engine.
2.1.2 Bio-syngas post-treatment
The biomass is cracker-cleaved at high ambient temperatures to yield crude bio-syngas containing mainly H2, CO, CO2, and CH4 in addition to other non-target gases. Small amounts of acidic gases and heavy metal impurities are present in the bio-syngas, which limits the downstream applications of the bio-syngas. To overcome this problem, in this project two different processes were used to purify the bio-syngas, Selexol and the water scrubber processes respectively. The bio-syngas composition and LHV values through two distinct syngas post-treatment processes are presented in Table 3. As we can see, both the Selexol and water scrubber processes provide excellent adsorption of impurity gases. Essentially, the only difference between the two processes is the ability to adsorb carbon dioxide, which is not as effective in water scrubber due to the low solubility of carbon dioxide in water. By absorbing CO2, the Selexol process increases the amount of flammable gas per unit volume, which increases the bio-syngas LHV value of the gas from 10.5 MJ/Nm3 to 16.7 MJ/Nm3 (Table 3). In addition, bio-syngas which meet here the conditions for transport through pipelines (more than 10 MJ/Nm3) is also suitable for use as a biofuel.
Table 3. Bio-syngas composition and LHV after syngas post-treatment
Items
|
Water scrubber
|
Selexol
|
Syngas composition
|
Volume fraction (vol.%)
|
Volume fraction (vol.%)
|
H2
|
62.5
|
68.7
|
CO
|
26.1
|
29.6
|
CO2
|
11.0
|
1.3
|
CH4
|
0.3
|
0.3
|
Syngas LHV (MJ/Nm3)
|
11.7
|
16.7
|
2.2 Techno-economic Analysis
As part of this study, a techno-economic evaluation was achieved to assess the costs of producing bio-syngas from biomass at an industrial scale. Based on technical and financial input parameters, this assessment estimates total capital costs, operating costs, and revenues. The capital costs are defined as the sum of direct costs, indirect costs, and other costs related to this project. Deduct the by-product credit from the total of the capital costs and the operating costs to get the total annual production costs. Finally, the sum annual manufacturing cost is divided by the total annual bio-syngas production to obtain the bio-syngas production unit cost.
2.2.1 Total Cost of Investment (TCI)
The TCI is all the costs incurred in making the investment, which includes the cost of investment, plus workers' wages, taxes, licenses and transaction-related fees. In order to calculate the direct cost, it is imperative to determine the enterprise's scale before calculating its direct costs, which for this study is defined as 10MW, meaning around 50 tons of biomass are processed per day. The cost estimation for the major equipment used in this project are shown in Table 4.
Table 4. Major equipment cost estimation
Op.1 (USD/kW)
|
Op.2 (USD/kW)
|
Biomass power generation
(USD/kW)
|
Biomass pre-treatment [29]
|
|
Handling
|
33
|
Drying
|
42
|
Gasification process
|
Gasifier
|
1184 [30]
|
Particles removal
|
44
|
Tar removal
|
4
|
Gas turbine
|
237
|
Heat Recovery Steam Generators
(HRSG)
|
76
|
Steam cycle
|
250
|
Heat exchange
|
180 [31]
|
Syngas cleanup and conditioning
|
Op.1
|
Op.2
|
Compressor
|
47
|
Compressor
|
47
|
Selexol
|
2885 [32]
|
Water scrubber
|
250 [33]
|
Total :
|
4982
|
|
2347
|
4000-7000 [34]
|
Table 4 summarizes the estimation of the major facility costs for the biomass gasification with water scrubber and the Selexol process, respectively. Meanwhile, the major facility costs for the biomass power generation system are also shown in Table 4. Biomass gasification coupled to Selexol process treatment results in a significant increase in equipment investment costs with a total cost of up to 4,982 USD/kW. Among them, the Selexol process equipment costs by itself 2,932 USD/kW, representing 58.85% of the total investment cost (as presented in Figure 4). In that context, Selexol process appeared to give better results through carbon dioxide adsorption but with higher costs; which results in a biomass gasification system being more expensive than a simple biomass power generation system. Due to this, biomass combustion for electricity generation takes precedence over biomass gasification for biomass applications. On the contrary, with water scrubber as syngas post-treatment, the total capital investment is only 2,597 USD/kW, and the investment in syngas post-treatment only accounts for 12.65% of the total equipment cost (as presented in Figure 5). There is a much lower equipment investment cost for biomass gasification with water scrubber compared with biomass combustion for power generation and it is the cheapest of the three processes. However, in the framework of sustainable energy development, and with governmental assistance to companies, the total cost of a project, although important, is no longer as decisive as before. Thus, a more expensive project but with a more interesting carbon footprint could be kept.
2.2.2 Product cost estimation
In order for start-up businesses to succeed, estimating production costs is essential. Not only does it determine the investment items and production cost, but it will also be a factor in the final end-user price. The profit margin a business can achieve can be affected by this product cost estimation. It is advisable to match all parameters with the actual price when calculating the production cost estimation, so that the results can be used as a reference. Key parameters defined for calculating the cost of bio-syngas production are presented in Table 5.
Table 5. Assumptions of bio-syngas production cost estimation
Items
|
Assumption
|
1. Raw material (biomass) (RM)
|
60 USD/ton
|
2. Utilities (electricity, heat, steam) (U)
|
Gasifier:250-350 kWh/ton*
Selexol: 28 USD/ton [32]
Water scrubber:20000 $/yr
|
3. Operating and maintenance (OM)
|
3.1 Labor wages
|
60,000 $/labor/year, 30 personnel
|
3.2 Maintenance
|
5 per cent of total capital investment
|
3.3 Repair supplies
|
15 per cent of maintenance and repairs
|
3.4 Laboratory
|
15 per cent of operating labor
|
4. Royalties (R)
|
1 per cent of total product cost
|
5. Depreciation (D)
|
15 per cent of total capital investment
|
6. Regional taxes and insurance (RI)
|
2 per cent of total capital investment
|
7. Plant overhead (PO)
|
50 per cent of labor wages
|
8. General expenses (GE)
|
8.1 Administrative cost
|
1 per cent of production cost
|
8.2 Distribution and marketing
|
1 per cent of production cost
|
8.3 Research
|
5 per cent of production cost
|
9. Total Operating cost (TPC)
|
RM+U+OM+R+D+RI+PO+GE
|
* The exergy efficiency of the gasifier reaches 40-50%, which requires an additional electrical energy supplement with a power consumption of 250-350 kWh/ton [28].
During the economic analysis, a number of parameters were defined to facilitate economic calculations. Due to CO2 emission restrictions, bioenergy is becoming increasingly important worldwide. In this study, as a means of stimulating bioenergy research and development, income tax rates and interest rates were defined as 0% as presented in Table 6. By the way, according to our previous research, if the income tax rate and interest rate are taken into account, the profits of bioenergy will be taken away by them, which makes bioenergy very expensive and difficult to promote the application of bioenergy [35].
Table 6. Economic hypotheses for total bio-syngas product cost estimation
Item
|
Economic assumptions
|
1. Project cycle
|
30 years
|
2. Factory up-time
|
350 days/year
|
3. Construction phase
|
3 years
|
4. Corporate income tax rate
|
0%
|
5. Interest rate
|
0%
|
6. Syngas price
|
0.55 $/Nm3
|
7. CO2 emissions reduction (tonnes)
|
0.76 t(CO2) /t(biomass) [36]
|
2.3 Economic evaluation results
Table 7. The results of the economic analysis of Op.1, Op.2 and biomass power generation
Item
|
Op.1
|
Op.2
|
Biomass power generation
|
Biomass power generation prices ($/kWh)
|
-
|
-
|
0.15-0.21 [37, 38]
|
Bio-syngas price
($/Nm3)
|
2.15
|
1.34
|
Equal to 1.58-2.21
|
*1NM3 natural gas calorific value equals 10.55 kWh of electricity
According to the outcome from the Aspen plus model and by the analyses of economic viability of two different syngas post-treatment processes using Selexol and water scrubber, we found that the estimation result of the unit cost of bio-syngas production was 2.15 $/Nm3 and 1.34 $/Nm3, respectively (as presented in Table 7). The use of Selexol post-treatment process increases the cost of capital investment, which could be mainly explained by the need for chemicals to absorb acidic gases. As a result, the unit cost of bio-syngas production increases to 2.15 $/Nm3, which is similar to the unit cost of bio-syngas production in previous studies using CO2 separation technology (2.43 $/Nm3) [39]. When bio-syngas is post-treated by water scrubbers, the bio-syngas production cost is reduced to only 1.34 $/Nm3. Previous studies have reported that producing bio-syngas from biomass costs 1.217 $/Nm3, whereas post-treatment of the syngas with water scrubber process slightly increases cost to 1.34 $/Nm3 [40]. In comparison with biomass power generation systems, when the syngas is post-treated by Selexol, the production cost of bio-syngas is higher than that of biomass power generation systems (The levelized cost of electricity of biomass for electricity generation ranges from a low of 1.58 $/Nm3 to a high of 2.21 $/Nm3). Therefore, biomass for power generation systems as a method of generating power has become the most preferred application of biomass. In comparison, bio-syngas is less expensive than that of biomass for power generation when water scrubber is used for syngas post-treatment. In terms of economics, this represents a breakthrough in biomass applications.
2.4 Sensitivity analysis
In an effort to promote bioenergy development, the government provides a variety of subsidies, such as tax breaks, grants, loans, and loan guarantees. In addition to encouraging bioenergy application, these stimulus policies will bring down the cost of biofuels, reduce dependence on fossil fuels, and preserve the environment. The stimulus policies will be used to subsidize the enterprise and lower the production costs of the firms, which in turn will reduce bio-syngas production costs. In this study, the impact of different factors on the unit cost of bio-syngas produced from a system that uses gasification and water scrubbing was investigated through a sensitivity analysis (e.g. biomass price, carbon tax and carbon credits).
2.4.1 Effect of biomass incentive on bio-syngas price
Using biomass as a sustainable and effective means of reducing greenhouse gas emissions, thus biomass energy can make a significant contribution to the reduction of fossil fuel dependency and the creation of alternative energy use options and feasible economic opportunities. An evaluation was conducted to assess the impact of biomass incentives on the cost of bio-syngas production. It was expected that biomass feedstock cost reductions would have an impact on bio-syngas production costs (as shown in Figure 6). By reducing biomass prices by 10 $/ton, bio-syngas production costs would fall by about 0.03 $/Nm3. Consequently, bio-syngas production cost dropped from 1.34 $/Nm3 to 1.23 $/Nm3 after biomass prices dropped from 60 $/ton to 20 $/ton. As we can observe here, bio-syngas price seems to be largely determined by labor, energy consumption and equipment involved in biomass preparation and processing.
2.4.2 The effect of carbon tax on bio-syngas price
Imposing a carbon tax would enhance the competitiveness of bioenergy production. Currently, biomass is more than three times as expensive as fossil fuels, which means a carbon tax of about $8/ton of CO2 generated by coal power would be necessary to make the fuel competitive with biomass [41]. An estimated carbon tax of $50 per metric ton on all energy-related carbon emissions is recommended [42]. Throughout the study, the carbon tax was floated between $10 per metric ton and 50 per metric ton, and the carbon tax was studied with regard to its impact on the cost of bio-syngas production. As shown in Figure 7, we can see that the carbon tax has a significant impact on bio-syngas production cost. Carbon tax increases from 10 to 50 per metric ton, reducing bio-syngas production costs from 1.20 $/Nm3 to 1.01 $/Nm3. The government of Canada has released an update to the “pan-Canadian Approach to Pricing Carbon Pollution” for 2023-2030 with the benchmark in 2023 increasing by C$ 15 (US$ 11.54) each year to C$170 (US$130.77) in 2030 [43]. Increasing the carbon tax price to 130.77 US$ /ton will make biomass energy competitive with traditional fossil fuels.
2.4.3 The effect of carbon credit on bio-syngas price
Carbon credit is a permit that allows enterprises to emit limited amounts of greenhouse gases (such as CO2) into the atmosphere. By containing enterprises to reduce their greenhouse gas emissions, a carbon credit system helps enterprises worldwide to emit greenhouse gases and reduce global warming. The effect of carbon credit would lead to a reduction in bio-syngas production cost. It is estimated that most carbon credits are priced below the $40-80 per metric ton of carbon dioxide emitted necessary to keep global warming within a 2-point degree range [44]. This study examined the impact of carbon credits on bio-syngas production cost by examining the price of carbon credits from $10 to $50 per metric ton (As shown in Figure 8). Increasing carbon credit prices from $10 to $50 per metric ton lowers the cost of producing biomass gas from 1.17 to 0.91$/Nm3. Biomass-based energy can be subsidized through carbon credits to help reduce its price and make it more widely available.
2.5 Bio-syngas applied to natural gas pipelines
A study of the effect of different bio-syngas percentages in natural gas on the LHV value and the natural gas price when the bio-syngas is injected into a pipeline. Currently, natural gas sells for 0.55 $/Nm3 and its LHV value is 36 MJ/Nm3. As the bio-syngas content of natural gas increases from 2% to 10%, the LHV value of blended natural gas declines from 36.0 MJ/Nm3 to 33.8 MJ/Nm3, while the price of blended natural gas increases from 0.55 $/Nm3 to 0.62 $/Nm3 (as presented in Figure 9). It is important to note that when the bio-syngas content in natural gas is 2%, the price of blended natural gas is at 0.56 $/Nm3 and the LHV value for blended natural gas is not greatly affected, at 35.6 MJ/Nm3, which has a negligible impact on the initial natural gas price (as presented in Figure 9). However, the natural gas use equivalent is large, and a 2% share already consumes a considerable amount of biomass resources. This magnitude of biomass applications could reduce global temperatures by two degrees Celsius, meeting the COP21’s target.