Business processes support the design and implementation of software as workflows of local and inter-organization activities. Tools provide the business process designer with modelling and execution facilities, but they barely provide formal analysis techniques. When one makes a process evolve, for example by refactoring it or by adding new features in it, it is important to be able to check whether, and how, this process has changed, and possibly correct evolution flaws. To reach this objective, we first present a model transformation from the BPMN standard notation to the LNT process algebra and LTS formal models. We then propose a set of relations for comparing business processes at the formal model level. With reference to related work, we propose a richer set of comparison primitives supporting renaming, refinement, property and context-awareness. We also support BPMN processes containing unbalanced structures among gateways. In order to make the checking of evolution convenient for business process designers, we have implemented tool support for our approach as a web application.