A method for dimensioning and erecting a process plant for carrying out a chemical engineering process, namely an air separation plant or a natural gas plant for natural gas liquefaction, comprising a computer-implemented method for dimensioning the process plant, wherein a multiplicity of process simulations is carried out in parallel, in the course of each of which the process in the process plant is in each case simulated for a particular application case, wherein each application case is characterized by values of process plant variables and/or values of process parameters, wherein different values for the process plant variables characterize different process plant topologies and specific embodiment of the process plant, wherein the process parameters characterize operating cases in accordance with which the process plant can be run or in accordance with which the process is carried out in the process plant, wherein the multiplicity of process simulations is performed in parallel by solving equations underlying the multiplicity of process simulations as a common equation system in which at least two different load situations are contained, wherein, in the multiplicity of process simulations, values for the process plant variables and for the process parameters are determined in such a way that at least one predefined condition is met, wherein free values for process plant variables and/or process parameters are determined, and wherein dependent values for process plant variables and/or process parameters are determined from the free values for process plant variables and/or process parameters, wherein a dependent value of a process plant variable or of a process parameter in one of the multiplicity of process simulations depends upon a free value of a process plant variable or of a process parameter in another of the multiplicity of process simulations, wherein dependent values relate to constructive parameters, namely process plant variables, which are accessible to the optimization once as a free value, but are the same in all process simulations and therefore dependent upon the first value in the other process simulations, namely are identical to it, wherein the multiplicity of process simulations is each assigned a weighting factor which characterizes the weight of a certain load situation in the overall operation, wherein a gradient-based optimization method is used for the optimal selection of the free values, which optimization method is based upon the evaluation of an analytical or numerically generated Jacobian matrix, wherein the process plant is erected and put into operation at a location in accordance with the selected dimensioning. wherein a multiplicity of process simulations is carried out in parallel, in the course of each of which the process in the process plant is in each case simulated for a particular application case, wherein each application case is characterized by values of process plant variables and/or values of process parameters, wherein different values for the process plant variables characterize different process plant topologies and specific embodiment of the process plant, wherein the process parameters characterize operating cases in accordance with which the process plant can be run or in accordance with which the process is carried out in the process plant, wherein the multiplicity of process simulations is performed in parallel by solving equations underlying the multiplicity of process simulations as a common equation system in which at least two different load situations are contained, wherein, in the multiplicity of process simulations, values for the process plant variables and for the process parameters are determined in such a way that at least one predefined condition is met, wherein free values for process plant variables and/or process parameters are determined, and wherein dependent values for process plant variables and/or process parameters are determined from the free values for process plant variables and/or process parameters, wherein a dependent value of a process plant variable or of a process parameter in one of the multiplicity of process simulations depends upon a free value of a process plant variable or of a process parameter in another of the multiplicity of process simulations, wherein dependent values relate to constructive parameters, namely process plant variables, which are accessible to the optimization once as a free value, but are the same in all process simulations and therefore dependent upon the first value in the other process simulations, namely are identical to it, wherein the multiplicity of process simulations is each assigned a weighting factor which characterizes the weight of a certain load situation in the overall operation, wherein a gradient-based optimization method is used for the optimal selection of the free values, which optimization method is based upon the evaluation of an analytical or numerically generated Jacobian matrix, wherein the process plant is erected and put into operation at a location in accordance with the selected dimensioning.