The production of oleo chemicals creates crude glycerine as a co-product, which is a solution of around 85% glycerine and 15% water plus contaminants. Pure glycerine has over 1,500 known end uses, for instance, in cosmetics, toiletries, personal care, drugs, and food products. However, the processing necessary to make this pure form is intensive, consumes high amounts of energy, and uses aggressive chemicals such as phosphoric acid and caustic soda that are recovered as waste or potentially discharged into surface water. Waste streams from glycerine refining, such as salts and non-reusable residues including heavy metals, are ultimately dumped in old salt mines. In addition, applications of pure glycerine only require small amounts, so supply greatly exceeds crude glycerine demand. Therefore, alternative uses of low-value crude glycerine are desirable to avoid it becoming a waste product in the future.
The QUARTERBACK for LIFE project's main objective is to mitigate the environmental consequences of the production of crude glycerine in the oleochemical industry. The aim is to demonstrate, in the first full-scale application of its kind, both the technical and economic feasibility of operating an integrated process in which crude glycerine is used as the only feedstock for an anaerobic digestion process in order to produce biogas for local use. This innovative process will enable oleochemical producers to meet part of their energy consumption with a carbon-neutral biofuel that enables a 25% (12,000 tonnes CO2/year) reduction in the facility's greenhouse gas emissions.
|Old situation||New situation|
Ultimately, the anaerobic glycerine digestion plant will replace a multistage concentration plant that uses steam to evaporate water from the glycerine-water mixture produced by hydrolysis of fats and oils.
In the new situation, following depressurization, the 10-15% glycerine mixture will be pumped to a buffer tank in the digestion plant at a temperature of more than 85ºC. After cooling to the required 37 ºC the stream will be charged into the two mesophilic anaerobic digesters of 3.500 m3 each. Over 90% of the COD in the feed stream is expected to be converted to a very clean biogas. Glycerine-water contains very little sulphur or other contaminants resulting in an almost sulphur free biogas is. The biogas is cooled, compressed, heated and filtered with carbon black and sent to the nearby boilerhouse/CHP area by pipeline.
Various nutrients will be added to sustain the biology in the digesters.
For emergency purposes a ground ("invisible") flare is installed to discharge surplus biogas
The digester outlet stream is degassed in an intermediate buffer tank and subsequently pumped to a decanter to separate digestion sludge from the main digestate stream. In turn, this stream is treated in the existing and modified aerobic effluent treatment plant prior to discharge into the river, combined with the existing effluent stream. The sludge is sent to an external contractor for composting. The effluent treatment plant has been equipped with new aeration elements to reduce energy consumption.
A new 2000kWe gas engine will be installed in the utility area. This reciprocating engine will convert biogas, and when applicable also natural gas, into electricity and heat. Heat is absorbed into a new warm water system with a start temperature of 90ºC. This warm water will be used for heating of product storage tanks, thus replacing the present low-pressure steam heating. The electricity will be used on-site for the regular production processes.
The flue gas from the engine will be treated by a catalytic DeNOx system to reduce nitrous oxides emission and will be cooled to 90 ºC or lower to recover as much energy as possible.
Another main item in the project is the modifications done to the site main high-pressure steam boiler. Originally this boiler was an auxiliary fired waste heat boiler, combined with a gas turbine-generator into a CHP system. After removal of the turbine, the opportunity arose to increase the boiler thermal efficiency by 10%. This has been achieved by replacing the burners, adapting these simultaneously for burning biogas, by downsizing and relocating the main air fan and by installing a new control system using excess oxygen in the flue gas for air-to-fuel ratio control.
The objective is to achieve a 12.000 ton/a, i.e. 25% reduction of CO2 emission: "Quarterback". Baseline is the Croda Gouda site energy consumption of 2012 with the previous CHP unit fully operative. The reduction is related to the volume of glycerine produced but for the 2013 volume would consists of:
|Replacement of natural gas by biogas||10%|
|Steam consumption reduction by decommissioning of glycerine concentration||8%|
|Electricity savings ETP, concentration and boilerhouse||1%|
|Increase due to electricity from grid||-17%|