JUSTICE LYTTON delivered the opinion of the court:

Plaintiffs, Central Illinois Light Company and Freeman UnitedCoal Mining Co. (together, CILCO), applied to the defendant,Illinois Department of Revenue, for a pollution control facilityexemption for their purchases of coal. CILCO claimed that becauseits coal produced electricity that powered a pollution controlsystem, the coal should be exempt from the Illinois Use Tax Act(Act). The Department denied the exemption, finding that theprimary purpose of the coal was not pollution control. CILCOappealed the decision to the circuit court. The circuit courtreversed the administrative decision. We reverse the judgment ofthe circuit court and confirm the ruling of the Department.

At the administrative proceeding, the parties waived anevidentiary hearing, and, instead, stipulated to certain relevantfacts. The parties agreed that CILCO, a utility company, operatestwo coal-fired power plants in Illinois known as the E.D. Edwardsand Duck Creek plants. When the coal at these plants is burned, itproduces emissions known as "flue gas," a discharge that has beenclassified as a pollutant by both the Illinois and federalEnvironmental Protection Agencies. CILCO employs two types ofpollution control devices at these plants: an electrostaticprecipitator at the Edwards facility and a precipitator inconjunction with a sulfur dioxide scrubber at the Duck Creek plant.Both devices constitute "pollution control facilities" as definedby the Act. 35 ILCS 105/2a (West 2000). The pollution controlfacilities operate continuously through electricity provided byCILCO. CILCO can compute how much additional electricity it mustproduce to power the devices.

Based on these stipulated facts, CILCO claimed an exemptionfrom the Illinois use tax only on the coal needed to produceelectricity to power the pollution control devices. CILCO assertedthat the coal qualified as part of a pollution control facility,which is specifically exempted under the Act. The Department citedthe "primary purpose" test from the Act and argued that for thecoal to be exempt from use tax, its primary purpose must bepollution control. The matter was argued before an administrativelaw judge.

The administrative law judge agreed with the Department anddetermined that CILCO failed to establish that the coal had as its"'primary purpose' the abatement of pollution" and recommended thatthe exemption be denied. The Department accepted the ALJ'sfindings of fact and application of the law and denied theexemption. CILCO sought review in the circuit court. The circuitcourt determined that the Department's decision to deny theexemption was clearly erroneous and entered judgment in favor ofCILCO and against the Department of Revenue.

STANDARD OF REVIEW

In reviewing a final decision under administrative review law,we review the agency's finding, not the circuit court'sdetermination. Metropolitan Airport Auth. v. Prop. Tax Appeal Bd.,307 Ill. App. 3d 52, 55 (1999). An agency's determination of factwill be disturbed only if it is against the manifest weight of theevidence. Abrahamson v. Illinois Department of ProfessionalRegulation, 153 Ill. 2d 76, 88 (1992). Questions of law, however,are not entitled to deference and are reviewed de novo. EnviriteCorp. v. Illinois Environmental Protection Agency, 158 Ill. 2d 210,214 (1994). Our supreme court held that a case that involves theexamination of the legal effect of a set of given facts is aquestion of mixed law and fact, and therefore should not beoverturned unless clearly erroneous. City of Belvidere v. IllinoisState Labor Relations Board, 181 Ill. 2d 191, 205 (1998).

The Department argues that we must review this case under aclearly erroneous standard, since a question of mixed law and factexists. To decide this case, we must only determine whether the Actexempts coal burned to power pollution control facilities. Sincethe issue is one of statutory interpretation, it must be reviewedunder a de novo standard. See City of Belvidere, 181 Ill. 2d at205. However, in arriving at our determination in this case, theagency's determination will remain "relevant" to our analysis. SeeBranson v. Department of Revenue, 168 Ill. 2d 247, 254 (1995).

ANALYSIS

I.

The Department argues that the primary purpose of the coal isto produce energy, not control pollution. Statutes imposing taxliability are generally construed against the state and in favor ofthe taxpayer (People Who Care v. Tax Objectors, 193 Ill. 2d 490,496 (2000)). However, statutory exemptions to taxation arestrictly construed in favor of taxation. Chicago Bar Ass'n v.Department of Revenue, 163 Ill. 2d 290, 301 (1994). The partyseeking the exemption bears the burden of clearly and conclusivelyproving it is entitled to the exemption. Chicago Bar Ass'n, 163Ill. 2d at 300. All debatable questions must be analyzed in favorof taxation. Wyndemere Retirement Community v. Department ofRevenue, 274 Ill. App. 3d 455, 459 (1995).

A tax is imposed "upon the privilege of using in this Statetangible personal property purchased at retail from a retailer." 35 ILCS 105/3 (West 2000). However, section 2a of the Act exemptspollution control facilities by removing those facilities from thedefinition of tangible personal property under the statute. 35ILCS 105/2a (West 2000). "Pollution control facilities" are definedas "any system, method, construction, device or applianceappurtenant thereto sold or used or intended for the primarypurpose of eliminating, preventing, or reducing air and waterpollution ... or for the primary purpose of treating, pretreating,modifying or disposing of any potential solid, liquid or gaseouspollutant..." 35 ILCS 105/2a (West 2000).

The pollution control facility tax exemption is governed bythe "primary purpose" test. Du-Mont Ventilating Co. v. Departmentof Revenue, 73 Ill. 2d 243, 248 (1978). The primary purpose of theproperty for which the exemption is sought must be pollutioncontrol or abatement. Central Illinois Public Service Co. v.Department of Revenue, 158 Ill. App. 3d 763, 768 (1987). The testis not satisfied merely upon proof that the use of certain tangiblepersonal property results in pollution control. Shell Oil Co. v.Department of Revenue, 117 Ill. App. 3d 1049, 1053 (1983). Onlyproperty directly involved in pollution abatement qualifies for theexemption. Central Illinois Public Service Co., 158 Ill. App. 3dat 768.

Primary is defined as "original,""fundamental," and "basic."Webster's Third New International Dictionary 1800 (1986). Underthis definition, the primary purpose of the coal burned by CILCO isnot the abatement or control of pollution. The primary purpose ofthe coal is to produce electricity. The electricity powers thepollution control system, which results in a decreased output offlue gas. CILCO claims that because burning the coal eventuallyresults in pollution control, the end result is sufficient toqualify the coal for the exemption. However, if the primarypurpose of the coal is not pollution control, any resultingbenefits are only adventitious, and the coal is not exempt from thetax. Any other outcome is contrary to the general rule that taxexemptions are construed against the taxpayer and in favor oftaxation. See Chicago Bar Ass'n v. Department of Revenue, 163 Ill.2d 290, 301 (1994).

CILCO cites us to Wesko Plating, Inc. v. Department ofRevenue, 222 Ill. App. 3d 422 (1991), where the Department hadpromulgated a regulation which specifically excluded chemicals usedin pollution control equipment from the exemption. On appeal, thecourt held that the regulation exceeded the Department'sadministrative authority and improperly circumscribed the statutoryexemption. Wesko, 222 Ill. App. 3d at 426. In its analysis of thestatute, the court found that because the chemicals introduced intoholding tanks eliminated pollutants through chemical reactions,they were integral to the pollution control system. The courtaffirmed the circuit court's decision to grant the exemption. Wesko, 222 Ill. App. 3d at 426-27.

There are two important distinctions between this case andWesko. In Wesko, the primary, if not sole purpose of the chemicalsin the system was to reduce pollution. In this case, the coal doesnothing to directly reduce pollution. Furthermore, Wesko struckdown a regulation imposing a blanket prohibition against theexemption of chemicals from the use tax. The issue before us, onthe other hand, is statutory, i.e., whether pollution control isthe primary purpose of the coal under section 2A of the Act.

CILCO also relies on Beelman Truck Co. v. Cosentino, 253 Ill.App. 3d 420 (1993). There, the court granted an exemption topickup trucks used by the transporter of hazardous waste to escortdump trucks carrying such waste, and also to carry any equipmentthat could be used to clean or contain any waste spill. Beelman,253 Ill. App. 3d at 421. The court found that the trucksconstituted a system or method of eliminating, preventing orreducing pollution, and thus were components of the overallpollution control system. Beelman, 253 Ill. App. 3d at 426.

Beelman is also distinguishable. The primary purpose of thetrucks was to reduce, control and prevent pollution by actuallyremoving pollutants. Here, the primary purpose of the coal was toproduce electricity. Furthermore, the trucks were not granted theexemption merely because they were components of a system, butbecause their purpose was integral to the disposal of pollutants.

Here, the coal is not a constituent part of CILCO's pollutioncontrol system. Thus, we agree with the Department's finding thatthe primary purpose of the coal is not pollution control.

II.

CILCO also argues that the primary purpose test is notapplicable to this case. CILCO reasons that but for the productionof energy from the burning of coal, the pollution control deviceswould not operate; therefore the coal is an integral part of thepollution control system. This "but for" test has been rejected byour own supreme court. Du-Mont Ventilating Company v. Departmentof Revenue, 73 Ill. 2d 243, 248 (1978); Beelman Truck Co. v.Cosentino, 253 Ill. App. 3d 420 (1993). In Du-Mont, the supremecourt mandated "primary purpose" as the appropriate test todetermine which property is exempt from the use tax. 73 Ill. 2d at248 (1978). Our court is bound to follow the rulings of theIllinois Supreme Court. People v. Wilson, 331 Ill. App. 3d 434,441 (2002). Because we have already determined that the primarypurpose of the coal is to produce heat, not to control pollution,the coal cannot be exempted from the tax.

III.

Next, CILCO complains that the Department promulgated aregulation that impermissibly limited the Act by excluding the fuelnecessary for operating pollution control facilities from thestatutory definition. See 86 Ill. Admin. Code 130.335 (2000). However, the administrative law judge clearly stated that herdecision was not based on the regulation. Because theadministrative law judge based her decision solely on theapplication of the Act to the facts, the regulation is not atissue, and this court will not review its validity.

IV.

Last, CILCO argues that since its systems have been or will becertified by the Illinois and federal Environmental ProtectionAgencies as pollution control facilities within the statutorymeaning of the Act, such certification is conclusive evidence thatthe primary purpose of those facilities is pollution control. Theagencies' certification, however, applies to the primary purpose ofthe pollution control facilities, not the coal burned to producethe electricity that powers them. The certification is notrelevant to the issue in this case.

CONCLUSION

The judgment of the circuit court of Peoria County is reversedand the decision of the Department is confirmed.

Circuit court judgment reversed, Department's decisionconfirmed.

HOLDRIDGE and SLATER, JJ., concur.