صفحه محصول - پاورپوینت با عنوان واکنش های شیمیایی

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واکنش های شیمیایی 2 فرایند احتراق یک واکنش شیمیایی است که در آن سوخت، اکسید می شود و انرژی آزاد می گردد. سوخت ها معمولا از ترکیبات یا مخلوط هایی شامل کربن و هیدروژن تشکیل یافته اند. مثال هایی از سوخت های هیدروکربنی: CH4 Methane C8H18 Octane Coal Mixture of C, H2, S, O2, N2 and non-combustibles در این بحث ما تنها واکنش های کامل را در نظر می گیریم. اجزای شرکت کننده در فرایند را قبل از انجام فرایند، واکنشگر (reactants) و بعد از واکنش محصول احتراق (products) می نامند. 3 فرایند احتراق، کامل یا استویکیومتریک نامیده می شود وقتی همه کربن و هیدروژن موجود در سوخت بسوزند و به ترتیب به دی اکسید کربن و آب تبدیل گردند. این دو واکنش احتراق کامل به این صورت می باشند. Example 15-1 A complete combustion of octane in oxygen is represented by the balanced combustion equation. The balanced combustion equation is obtained by making sure we have the same number of atoms of each element on both sides of the equation. That is, we make sure the mass is conserved. Note we often can balance the C and H for complete combustion by inspection. 4 The amount of oxygen is found from the oxygen balance. It is better to conserve species on a monatomic basis as shown for the oxygen balance. Note: Mole numbers are not conserved, but we have conserved the mass on a total basis as well as a specie basis. The complete combustion process is also called the stoichiometric combustion, and all coefficients are called the stoichiometric coefficients. In most combustion processes, oxygen is supplied in the form of air rather than pure oxygen. Air is assumed to be 21 percent oxygen and 79 percent nitrogen on a volume basis. For ideal gas mixtures, percent by volume is equal to percent by moles. Thus, for each mole of oxygen in air, there exists 79/21 = 3.76 moles of nitrogen. Therefore, complete or theoretical combustion of octane with air can be written as 5 Air-Fuel Ratio Since the total moles of a mixture are equal to the sum of moles of each component, there are 12.5(1 + 3.76) = 59.5 moles of air required for each mole of fuel for the complete combustion process. Often complete combustion of the fuel will not occur unless there is an excess of air present greater than just the theoretical air required for complete combustion. To determine the amount of excess air supplied for a combustion process, let us define the air-fuel ratio AF as Thus, for the above example, the theoretical air-fuel ratio is