Power-to-ammonia (P2A) provides a carbon-free alternative to conventional ammonia production by replacing fossil-based feedstocks with electrolytic hydrogen and nitrogen from air separation. For decentralized P2A systems, pressure swing adsorption (PSA) offers a flexible alternative to cryogenic air separation. However, its industrial implementations are largely proprietary, and open, first-principles models capable of simulating its cyclic, nonlinear transport are scarce in literature. This work presents a first-principles, dynamic, one-dimensional model of a PSA superstructure for nitrogen generation, formulated with thermodynamically consistent equations of state, coupling multicomponent mass, energy, and momentum balances with kinetically limited adsorption on carbon molecular sieves. The resulting system of partial differential-algebraic equations (PDAEs) is semi-discretized using the finite volume method, integrated using diagonally implicit Runge-Kutta methods, and cyclic steady states (CSS) are computed via shooting-based solution methods. The framework is implemented in Julia, combining analytical derivatives with automatic differentiation and utilizing sparse linear algebra for efficient solution of the arising large nonlinear systems. The framework is demonstrated on a two-bed PSA cycle for air separation, comparing spatial and temporal discretization strategies, CSS solution methods, and the effects of ideal versus real-gas thermodynamics on predicted nitrogen purity and recovery. The proposed framework establishes an extensible basis for PSA simulation and optimization.

翻译：电转氨技术通过用电解制氢和空气分离制氮替代化石基原料，为传统氨生产提供了一种无碳替代方案。对于分布式电转氨系统，变压吸附技术为低温空气分离提供了灵活替代方案。然而，其工业实现大多涉及专有技术，而能够模拟其循环非线性输运过程的开放式第一性原理模型在文献中较为稀缺。本文提出了一个基于第一性原理的变压吸附超结构动态一维制氮模型，该模型采用热力学一致的状态方程进行构建，耦合了多组分质量、能量和动量平衡与碳分子筛上的动力学受限吸附。由此产生的偏微分代数方程组采用有限体积法进行半离散化，利用对角隐式龙格-库塔方法进行积分，并通过打靶法计算循环稳态。该框架使用Julia语言实现，结合了解析导数与自动微分技术，并利用稀疏线性代数高效求解产生的大规模非线性系统。本文通过双床变压吸附空气分离循环对该框架进行了验证，比较了空间和时间离散化策略、循环稳态求解方法以及理想气体与实际气体热力学对预测氮纯度和回收率的影响。所提出的框架为变压吸附仿真与优化建立了可扩展的基础。