With 40 $\mathrm{mol\%}$ CO₂, the energy content of biogas is too low to be used as motor fuel. Motor-grade compressed bio-methane can be produced by direct methanation of biogas with the use of hydrogen. A direct methanation process is considered here as the pre-processing step of separating the biogas is avoided. A systematic staging method is applied to design the process to upgrade biogas to motor-grade bio-methane by maximizing the production of methane with the use of the least possible reaction volume and subject to a quality specification. Here, a once-through process is the target so as to avoid the post-processing separation of the product and recycling. The most promising design is a three-stage configuration with water condensation after each stage. Shell and tube reactors are considered to be less expensive than micro-channel reactors. All three stages are placed in a single shell with boiling water on the shell side. The proposed design is verified by rigorous simulation. The method makes process intensification of chemical reaction systems possible, which is here demonstrated for direct methanation of biogas.

有 40$\mathrm{摩尔\%}$二氧化碳₂，沼气的能量含量太低，不能用作汽车燃料。汽车级压缩生物甲烷可以通过使用氢气直接甲烷化沼气来生产。这里考虑直接甲烷化过程，因为避免了分离沼气的预处理步骤。应用系统的分级方法来设计将沼气升级为汽车级生物甲烷的过程，该过程通过使用尽可能少的反应体积和质量规范来最大限度地提高甲烷的产量。这里，目标是一次性处理，以避免产品的后处理分离和回收。最有前途的设计是三级配置，每级后都有水冷凝。管壳式反应器被认为比微通道反应器便宜。所有三个阶段都放置在一个壳中，壳侧有沸水。所提出的设计通过严格的仿真得到验证。该方法使化学反应系统的过程强化成为可能，这里证明了沼气的直接甲烷化。