Feasibility study on improved acetylation plant designs

In this project, the feasibility of developing a new plant for wood acetylation that can result in better Internal Rate of Returns (IRR) than current production plant is being studied.
Accsys Technologies PLC focuses on the development and commercialization of a range of wood modification technologies based upon the acetylation of solid wood and wood elements. In the company’s production facility in Arnhem, the Netherlands, normal wood boards are chemical modified to acetylated wood boards traded with brand name Accoya®. The Accoya © process consists of wood pre-vacuum, reactor filling with acetic anhydride, impregnation at high pressure, reactor emptying, acetylation, thermal extraction of unreacted acetic anhydride and acetic acid which is formed as by-product of acetylation reaction and cooling. Both heating and cooling are carried out with external gas loops in which centrifugal fans and heating elements are incorporated. The external gas loops driven the flow of gas across wood batch located inside reactor to heat up/cool down batch through convective heating/cooling.
With the superior wood quality of Accoya® in terms of durability and dimensional stability, sales of Accoya® is boosting and the current production facility is reaching its capacity limit. Thus, the company wants to have a plant design that is better than the current system in terms of production capacity and capital investment. IRR is a parameter that summarizes these two factors and it is desired to have a new plant design that results in 10% enhancement in IRR.
To formulate a new plant design and to evaluate its feasibility, this project is divided into two phases: concept generation and selection phase and focused phase.
In concept generation and selection phase, Ontology Design is applied on the generating design concepts. The concepts are ranked among each other in terms of:
 Overall Capacity
 CAPEX per unit capacity
 OPEX per unit capacity
 Safety
 Product Quality
 Time to Develop
 Probability of Success
Increasing Reactor Diameter, Decoupled Drying with Vacuum Drying and Decoupled Drying with Superheated Steam are selected for further evaluation. Eventually, Decoupled Drying with Vacuum Drying is selected as the new design concept to be studied in the focused phase.
Decoupled Drying with Vacuum Drying refers to the approach of taking out wood batch that has just finished acetylation from reactor and moving it to a separate dryer. The capital investment on dryer system is expected to be lower than the reactor system and CAPEX can be saved.
This design concept is then evaluated in terms of technical feasibility and economic feasibility.
On technical feasibility, the ventilation needed to safely transferring wood batch with acetic acid and acetic anhydride embedded in between reactor and dryer is determined through an emission test.
On economic feasibility, suppliers for ATEX vacuum dryer and ATEX transfer system are identified and through detailed discussions, quotations on the two systems are obtained. They are €2.200.000 and €300.000 respectively. A CAPEX model is built to determine the fixed capital and total capital investment of decoupled drying system.
Scenarios on decoupled dryer are set based on conditions of wood during transfer (i.e. wood temperature and residual chemical contents), usage of thermocouples and ratio between number of reactors and number of dryers. Final candidates are selected among the scenarios in terms of fixed capital per unit capacity and big systems (2 reactors plus 3 dryers or 3 reactors with 2 dryers) are found to outperform the current system and are attractive.
IRRs calculated are 35% to 38%, more than 10% higher than the IRR of the base case, which is 25%. Dryer Cost, Additional Cost on Dryer and Transfer System Cost are the three big uncertainties in IRR calculations but sensitivity analysis shows that the improvement is still higher than 8% with uncertainties taken into account.