PROJECT DESCRIPTION
BACKGROUND
In one of the processes for the production of potato starch derivatives, ethylene oxide (CH2CH2O) is used to modify the starch. Ethylene oxide is a toxic, inflammable and potentially carcinogenic chemical, and therefore, the emission of the ethylene oxide from the process after the reaction presents a problem. From the reaction tanks the slurry of modified starch, some others solids, such as salts, and the remaining ethylene oxide are pumped into a buffer tank. To remove the salt the slurry is washed with water. In sequence the slurry is then dewatered on a vacuum filter and dried in a dryer. During washing, dewatering and drying the ethylene oxide is almost totally removed from the product. The wastewater from the washing process is carried to the wastewater treatment plant from where ethylene oxide enters the environment. The air from the dryer also emits a small amount of ethylene oxide into the environment. In total 88 tons/year of ethylene oxide is emitted. AVEBE planned a new installation for the production of starch derivatives to replace the two old production lines and to increase the production capacity. As part of this development, AVEBE also planned to put in place a system to prevent emissions of ethylene oxide. Since distillation, the “state of the art technology” for the removal of ethylene oxide, was not appropriate for the production of the starch derivates, AVEBE developed an alternative process based on the extraction of ethylene oxide from the product slurry in a spraying tower, followed by adsorption and conversion. In this so-called “green” process, emissions of ethylene oxide would be effectively eradicated. The objective was to reduce the concentration of ethylene oxide in the modified starch slurry to a maximum of 0,1 ppm. This Life project aimed to demonstrate the first full scale application of this alternative extraction process.
OBJECTIVES
The aim of the project was to demonstrate a new extraction process and to prevent the emission of ethylene oxide into the environment. The expected results were a final emission of ethylene oxide close to 0 tonnes per year, as compared to 88 tonnes per year at present. The initial technical solution was developed by AVEBE itself and was based on the use of a spraying tower. As a result of intense contact between the slurry and nitrogen-gas (N2) the ethylene oxide dissolves in the nitrogen-gas. This happens in batches. At the start of the removal process a concentration of about 1400 ppm (3 kg/m3) is reached. The slurry then circulates over storage tanks and the spraying tower, during which it is sprayed in the continuously purified nitrogen-gas until the concentration in the headspace is reduced to below 0,1 ppm. After this treatment the slurry is washed, dewatered and dried. It was expected that there would be no further emission of ethylene oxide from the washing water and exhaust air of the dryer. After extraction of the ethylene oxide the gas mixture of N2-gas and ethylene oxide is passed trough a solution of sulphuric acid (H2SO4). The ethylene oxide reacts to form ethylene glycol, also known as cooling fluid for engines. The sulphuric acid acts as a catalyst. The purified nitrogen-gas is reused in the process.
RESULTS
Before ordering the new installations AVEBE did a number of tests with an in-line spraying tower. Up to the purification process the results were as expected. However during treatment after this process, in the reactors and during the washing step, a minimum reversal took place from other chemicals in the slurry. The consequence of this was that the required reduction in ethylene oxide took alot longer than expected. Based on the capacity of the plant this meant that a much bigger installations would be required. It was therefore concluded that this technique would not achieve the project’s objectives, so AVEBE decided to undertake additional research. This research resulted in the development of a new process, acid disintegration, which would enable the beneficiary to meet the project’s emission reduction objective. However, a new problem occurred in July 2001. The foundations of the existing factory, where the new factory was to be partly integrated, appeared to be inadequate. In order to achieve a reduction in emissions AVEBE would therefore have to build a completely new plant. The project therefore ended on the original deadline (1st May 2002) before the actual construction of the plant had started. In August 2002 AVEBE took the decision to proceed with the building of the new K3 plant and to implement the new process, demonstrating its confidence in the acid disintegration process. Within the project period, the beneficiary was therefore not able to meet the objective (to demonstrate a new extraction process and to prevent the emission of ethylene oxide to the environment) because of the technical problems encountered. However, the beneficiary did find solutions to these technical problems: a new process (acid disintegration) was developed and a new plant was designed that meets the emission reduction targets originally set. However, since the formal and final guarantee for building the plant and demonstrating the new process only came after the project deadline, the new plant was not built within the framework of the Life project. The capacity of the project team to find solutions to the technical problems encountered has clearly been crucial to the implementation of the project. The beneficiary had to come up with a new solution (because of, among other things, its engagement with the environmental authorities) and proved to be extremely persevering. From an "end-of-pipe" solution the project became a new strategic production plant making use of process-integrated measures to achieve the emissions reduction objective. The project proved that the initial solution proposed would not achieve the desired objective. This is an important lesson for interested third parties, who can access this information via the database and the layman report. The environmental benefits of the new process, acid integration, are even better than those of the process originally proposed: AVEBE expects to reduce the emission of ethylene oxide, a toxic, inflammable and potential carcinogenic chemical, from 88t/a to nearly 0 t/a. The beneficiary furthermore requires fewer installations, uses less energy and the process requires less maintenance than the process originally proposed. When the new process is demonstrated at full scale, it could also be used at other plants. In Europe, about 110,000 tonnes of ethylene oxide and propylene oxide (a very similar chemical) are used every year. AVEBE uses about 800 t/a. Examples of other (significant) users in the EU are Emsland (D), Rocket (F), Amylem (B), Stadex (S), Raisio (FIN) and Lickerby Starkelsen (S). It is anticipated that the project could be reproduced 5 to 10 times in the EU starch sector, and 50 times in other industries.
