Technology for using a bio-mixture based on sewage sludge for energy production and agricultural purposes
Title of the offer
Technology for using a bio-mixture based on sewage sludge for energy production and agricultural purposes
Offer description
The subject matter of this Invitation is the technology for using a bio-mixture of sewage sludge and chopped straw for energy production and agricultural purposes. Due to the properties of mixture components, it was necessary to develop a device that allows applying them in adequate proportions, and can be adapted for use with a certified high-quality briquetting press. The analysis of briquette composition and of the combustion process made it possible to achieve the results intended. The project included the development of a bio-mixture feeder prototype. The material is fed with a screw feeder placed inside (at the bottom of) the tank. The device is equipped with a control system. Bio-mixture components were obtained and prepared so as to ensure adequate granularity and so they may be evenly discharged during operation of the briquetting machine. Pre-dried sludge was discharged in the form of a granulate; and straw was discharged in the chopped form. Once built, the prototype was calibrated for different settings of the control panel. This allowed to determine the relationship between feeder performance and the preset speed of the screw feeder engine. The prototype was installed on a certified briquette production line with a capacity of ca. 60 kg/h. Following this, the device was started up and the briquette production process was initiated. Different speed settings were applied for the screw feeder engine, resulting in differences in feeder performance and in mixture composition. The mixtures produced contained from 23% to 50% of sewage sludge and their humidity varied in the range of 14% to 24%. The study included performing structural strength tests for the briquettes in accordance with PN-EN ISO 17831-2:2016-02. The structural strength of briquettes varied in the range of 84% to 92% (87% on average). The briquettes made of the straw and sludge mixture had a similar structural strength to briquettes made exclusively of straw. The properties of bio-mixtures produced were also tested. The study found that the carbon content does not change together with the amount of sludge in the briquette, and is 45.1% on average; sulfur, hydrogen and chlorine content increases slightly (on average: 0.330%, 6.140% and 0.046%, respectively). In turn, as the sludge content increases, so does nitrogen content (up to ca. 6%), phosphorus content (up to ca. 2.5%), potassium content (up to ca. 1%) and ash content. The net calorific value of fuel made of the bio-mixture did not depend on the sludge content and was ca. 15.5 MJ/kg. The study also included testing the exhaust gas emissions during briquette combustion in the energy production process in accordance with PN-EN 303-5:2012. The presence of carbon oxides (ca. 2000 mg/m3), sulfur oxides (ca. 400 mg/m3) and nitrogen oxides (ca. 420 mg/m3) was detected. It was found that when adequately prepared, sludge (especially from small water treatment plants) can form a bio-mixture with chopped straw, be pressed into briquettes and be used for energy production or agricultural purposes.
Keywords
Technology for using a bio-mixture based on sewage
