This study aimed to evaluate the TEF (PyOL-based organic and plastic wastes) of a pilot plant in Malaysia. As oxidative pyrolysis used less energy to reach the pyrolysis temperature, using oxidative pyrolysis rather than pure N
2 pyrolysis produced significant flue gas savings. Conversely, the drawback of this method was lower liquid yield. Meanwhile, the pilot-scale pyrolysis system provided the information for this study has several limitations [
24]. These limitations included underestimating the raw material or energy costs and overestimating the product or service demands, which caused inaccurate profitability estimates. Changing policy and market conditions also impacted the assumptions made.
2.1. Oxidative Pyrolysis of OPW
Instead of using pure N
2 for pyrolysis, oxidative pyrolysis was applied, where non-oxidative thermal degradation and heterogeneous oxidation occurred simultaneously [
24]. This process was performed using air with flue gas for OPW pyrolysis. Exothermic reactions require oxygen from the air, generating heat for the endothermic pyrolysis reactions. Unlike laboratory studies, the heat for the pyrolysis process is caused by electrical heaters that are not economically viable.
Flue gas has a temperature of between 150 and 200 °C, which is generated by power plants or combustion processes. This gas is an untapped heat source for oxidative pyrolysis, which lowers operational costs and pure N2 consumption [
25,
26]. A local supplier set the price of N2 at USD 36 per kg (December 2021) or RM 6 per m
3 (January 2022) [
27]. Approximately 79% of flue gas is N
2, 14% is CO
2, and 7% is O
2. Compared to N
2-based pyrolysis, oxidative pyrolysis is anticipated to produce a higher gas output [
28]. For example, the waste-to-energy system utilizing pyrolysis of food waste assisted with CO
2 has increased CO generation. When CO
2 is used during the pyrolysis of plastics, the formation of polyaromatic hydrocarbons (PAH) and acidic chemicals are reduced compared to N
2-based pyrolysis [
29,
30]. This outcome is due to CO
2 hindering the aromatization and cyclization reactions while accelerating the thermal cracking of volatiles during pyrolysis. In addition, CO
2-assisted pyrolysis improves thermal efficiency, increases the breakdown and rearrangement of volatile products, and inhibits the reactivity of volatile organic compounds with gas [
31,
32].
2.2. Lifecycle Assessment (LCA) of the Pyrolysis System and Mitigated CO2
The CO
2 emission factors for a linear economy were collected from several studies where MSW was in a landfill, while chemicals were manufactured using fossil fuels (conventional routes). Furthermore, the CO
2 emissions per kg were compared to a circular economy-based scenario in which landfill-based MSW produced PyOL (extracted chemicals). For every 2500 tons of MSW, 3117 tons of CO
2 emissions were recorded daily based on the Bukit Beringin Landfill estimates in 2015 [
33]. This observation amounted to 1.25 kg of CO
2 per kg of MSW. The “Our World in Data” database contained carbon emission data related to food production [
34]. Consequently, shrimp, fish food, chicken meat, and beef produced 27, 14, 10, and 100 kg of CO
2 per kg of MSW, respectively. The CO
2 emission also reported high-value chemical production, ranging between 4 and 5 kg of CO
2 per kg of MSW using conventional and methane-based methods [
35].
2.3. TEF Study for a Commercial Pyrolysis Plant
A TEF study assessed the potential of establishing a commercial pyrolysis plant that generated value-added chemicals. This study was evaluated by sending survey forms to potential pyrolysis oil off-takers, involving BASF, PETRONAS Research Sdn. Bhd., Alam Flora, Jengka Advanced Renewable Energy Plant (JAREP), and other chemical companies (see
Figure 1). Three of the five comments concerned capital, collection, and operating costs.
Academics from Curtin University and Manchester University, United Kingdom, conducting TEF studies on industry-based pyrolysis were consulted in this study.
Figure 2 portrays the overall process of performing the TEF studies. Capital expense data were sourced from Fivga et al.’s study, which estimated the costs of waste plastic pyrolysis, material balances, energy needs, and utilities using process simulation software (Aspen HYSYS v8.6) [
36].
Figure 3 illustrates the formic acid, furfural, and phenol extraction methods [
10,
32,
37]. Although the capital expenditures for extracting these compounds were unknown, the average capacity and recent investment values in crude oil-to-chemicals (COTC) plants were utilized instead [
38]. The average capital cost was estimated to be RM 2722 per ton of PyOL based on the investment lists and capacities of COTC plants (see
Figure 4).
The TEF analysis was performed for pyrolysis plants handling MSW values of 20, 100, 1000, and 10,000 kg/h in response to Fivga et al.’s study [
36]. According to a Malaysian Performance Management and Delivery Unit study, the waste collection cost was approximately RM 150 per ton daily [
39]. The waste collection cost was lowered to meet each collector’s minimum wage (RM 1500 monthly). Therefore, these costs were reduced from RM 300 ton/day to RM 275, 150, and 100 ton/day for plant capacities of 20, 100, 1000, and 10,000 kg/h, respectively.
The pyrolysis plant data using flue gas as a pyrolysis agent and OPW as feedstock were not readily available. Thus, additional feasibility data were estimated using techno-economic analysis of pyrolysis plants employing woody biomass, rice husks, or plastics as feedstock. These data were obtained from institutions like the National Renewable Energy Laboratory (NREL) [
40,
41]. The pyrolysis fuel production cost for various plant capacities was then evaluated according to Fivga et al.’s study [
36]. Meanwhile, studies by Wright [
40], Jahirul [
42] and Islam [
43] provided the operating breakdown costs for labor, operation, and maintenance (OM) of the proposed pyrolysis plants with an annual operational time of 7008 h/yr. The OM cost involved clearing pipe blockages, repairing conveyors, compressors, and air distribution plates, maintaining pyrolysis agent systems, fixing pipe leaks, and a one-time payment for overhauling major equipment (heating system and large material handling equipment).
The total operational costs increased with plant capacity due to rising energy costs and the demand for consumables, such as liquid petroleum gas (LPG), to heat the reactor. In contrast, the operational costs per kg of OPW decreased when the labor costs did not increase linearly with plant capacity. The operating cost was hypothetically lower than plants that employed pure N2 as the pyrolysis agent. Although the proposed pyrolysis plant utilized flue gas for fluidization and pyrolysis processes, additional pumps and pipe insulations were necessary to raise the pressure while maintaining the temperature.
For plants with capacities of 1000 and 10,000 kg/h, using flue gas at an average temperature of 150 °C for heating the reactor to 350 °C decreased LPG consumption by between RM 40,009 and 400,098 annually. Interestingly, this flue gas-based process also prevented and reduced the CO
2 released into the atmosphere. Depending on the implementation of a domestic carbon trading mechanism and the carbon price (RM 35 to 150 per ton of CO
2), the flue gas fast pyrolysis system provided additional revenue if other carbon-emitting companies purchased carbon credits from the carbon offset of the pyrolysis system [
44].
The expected capital, OM expenditures, and revenue for two case studies were considered in the TEF analysis. The first case study demonstrated the PyOL as the sole product, which the PyOL costing approximately RM 0.60 per kg based on a local PyOL manufacturing company survey. Likewise, the pyrolysis technology used in this study yielded a 5% PyOL. A higher yield was also possible (20 to 30%) with low condensation temperatures (10 to −10 °C). Nonetheless, the low condensation temperature was assumed to be unavailable in the commercial plant owing to the high capital investment needed, producing lower PyOL due to the limitation of energy consumption. The second case study reported the chemical extractions of formic acid, furfural, and phenol from PyOLs through processes presented in several studies [
10,
32,
37]. These studies provided the estimated chemical yields with the estimated minimum value prices (obtained from the Chemical Book and Sigma-Aldrich or Merck websites) [
45,
46]. Hence, the values reported are presented as follows:
Yield of furfural: 1.0%, at RM 303/kg
Yield of formic acid: 8.4%, at RM 96/kg
Yield of phenol: 4.1%, at RM 437/kg
The specific unit pricing (expressed in RM/L) increased with order volume. Thus, the specific unit price for phenol, furfural, and formic acid was averaged over quantities ranging from 1 to 25 kg (or 1 to 25 L). The profitability per year (PF) was calculated as the total annual income minus the total yearly operating, maintenance, and utility costs (PF). Similarly, the actual cash flow per year (CFn) for Year n was calculated by multiplying PF with a present value factor (PVn) and a discount factor r of 8%. Therefore, the actual PF declines over time is as follows:
Since the construction and commissioning were supposed to take two years and the capital investment (CI) was set at Year n (where n = 0, 1, 2, …), Years 1 and 2 demonstrated no cash flow. From Years 3 to 8, the PV value decreased from 0.7938 (PV3) to 0.5403 (PV8). Subsequently, the net present value (
NPV) and internal rate of return (IRR) for each scenario are calculated as follows:
The is set to null to determine the IRR.