A chemical engineering firm has been tasked with designing a chemical reactor for the synthesis of ammonia gas from nitrogen and hydrogen gases. The plant requires a production of at least 1000 kg/h of ammonia gas, and the reactor should operate at a pressure of 200 atm and a temperature of 400°C. The student should determine the optimal size and design of the reactor by considering the reaction kinetics, thermodynamics, and fluid dynamics principles. The student should also select appropriate catalysts and determine the flow rate of the reactants required to achieve the desired production rate.

Question

A chemical engineering firm has been tasked with designing a chemical reactor for the synthesis of ammonia gas from nitrogen and hydrogen gases. The plant requires a production of at least 1000 kg/h of ammonia gas, and the reactor should operate at a pressure of 200 at

Answer 1

To design the chemical reactor for ammonia synthesis, we need to consider the following factors:1. Reaction kinetics: The rate of ammonia synthesis is given by the Haber-Bosch process, which is a reversible exothermic reaction:N2 g  + 3H2 g   2NH3 g The rate of this reaction depends on the temperature, pressure, and catalyst used. At 400C and 200 atm, the reaction rate will be relatively high, but the equilibrium conversion will be lower due to the exothermic nature of the reaction.2. Thermodynamics: The equilibrium constant  K  for the reaction can be determined using the Van't Hoff equation and the standard Gibbs free energy change  G  for the reaction:K = exp -G/RT At 400C  673 K  and 200 atm, the equilibrium constant can be calculated, which will give the equilibrium conversion of nitrogen and hydrogen to ammonia.3. Fluid dynamics: The flow rate of the reactants  nitrogen and hydrogen  should be determined to achieve the desired production rate of 1000 kg/h of ammonia. The stoichiometry of the reaction indicates that 1 mole of nitrogen reacts with 3 moles of hydrogen to produce 2 moles of ammonia. The molar flow rates of nitrogen and hydrogen can be calculated based on this stoichiometry and the desired ammonia production rate.4. Catalyst selection: The most commonly used catalyst for ammonia synthesis is iron with promoters such as potassium, aluminum, and calcium oxides. This catalyst has high activity and selectivity for ammonia synthesis under the given operating conditions.5. Reactor design: A packed-bed reactor is a suitable choice for this process, as it provides a high surface area for the catalyst and good contact between the reactants and catalyst. The size of the reactor can be determined by considering the reaction kinetics, equilibrium conversion, and reactant flow rates. The reactor volume can be calculated using the following equation:V = F_A0 * X /  -r_A where V is the reactor volume, F_A0 is the molar flow rate of nitrogen, X is the conversion of nitrogen, and -r_A is the rate of reaction per unit volume of the catalyst.By considering all these factors, the optimal size and design of the reactor can be determined, along with the flow rate of the reactants required to achieve the desired production rate of 1000 kg/h of ammonia.