As market demand forecasts will become more uncertain in the future it is necessary to develop new methods for plant design. New technologies allow combining the flexibility of a batch plant with the efficiency of a continuous production. To gain even more economic benefit intensified equipment is often designed as a module. The usage of equipment modules allows an easily and efficient increase of capacity. In this way a plant expansion close to the market is possible. Consideration of stepwise plant expansion is often limited to the copying of complete production lines. This approach results in high additional investment costs due to the loss of economy of scale. To overcome the limitations set by economy of scale, an equipment wise expansion strategy should be applied. By debottlenecking the capacity limits of the plant it is possible to adapt plant capacity very close to the changing environment and reduce the additional costs. Therefore, design of a modular plant must be combined with suitable economic evaluation methods for uncertain demand forecasts. In this work a framework for such a design based on predefined and standardized modules will be presented. The framework consists of two stages. The first stage is the selection of possible modular setups and suitable expansion strategies. Next these setups are evaluated in a real option analysis to investigate the economic performance in an uncertain market. The approach will be used to evaluate a multiproduct continuous plant. The main finding is that the economy of the modular plant depends under the given boundary conditions on the equipment item with the highest proportion on total investment costs and a high cost degression exponent. (C) 2014 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.