Gasification of meat and bone meal

Abstract

Meat and bone meal (MBM) is a byproduct of the rendering industries. It is found to be responsible for the transmission of bovine spongiform encephalopathy (BSE) in animals and is no longer used as a feed to animals. There are various methods for disposal of MBM such as land filling, incineration, combustion, pyrolysis and gasification. Gasification appears to be one of the best options. High temperature of gasification reaction destroys the potential BSE pathogens and produces gases which can be further used to produce valuable liquid chemicals by Fischer-Tropsch synthesis or to generate electricity. Gasification of meat and bone meal followed by thermal cracking/ reforming of tar was carried out using oxygen and steam separately at atmospheric pressure using a two-stage fixed bed reaction system in series. The first stage was used for the gasification and the second stage was used for thermal cracking/ reforming of tar.

Meat and bone meal was successfully gasified in the two-stage fixed bed reaction system using two different oxidants (oxygen and steam) separately. In gasification using oxygen, the effects of temperature (650 – 850 °C) of both stages, equivalence ratio (ER) (actual O2 supply/stoichiometric O2 required for complete combustion) (0.15 – 0.3) and the second stage packed bed height (40 – 100 mm) on the product (char, tar and gas) yield and gas (H2, CO, CO2, CH4, C2H4, C2H6, C3H6, C3H8) composition were studied. It was observed that the two-stage process increased hydrogen production from 7.3 to 22.3 vol. % (N2 free basis) and gas yield from 30.8 to 54.6 wt. % compared to single stage. Temperature and equivalence ratio had significant effects on the hydrogen production and product distribution. It was observed that higher gasification (850 °C) and cracking (850°C) reaction temperatures were favorable for higher gas yield of 52.2 wt. % at packed bed height of 60 mm and equivalence ratio of 0.2. The tar yield decreased from 18.6 wt. % to 14.2 wt. % and that of gas increased from 50.6 wt. % to 54.6 wt. % by changing the packed bed height of second stage from 40 to 100 mm while the gross heating value (GHV) of the product gas remained almost constant (16.2 – 16.5 MJ/m3).

In gasification using steam, effects of temperature (650 – 850 °C) of each stage, steam/MBM (wt/ wt) (0.4 -0.8), and packed bed height (40 -100 mm) in second stage on the product (Char, liquid and gas) distribution and gas (H2, CO, CO2, CH4, C2H4, other H/C) composition were studied. It was observed that higher reaction temperature (850 °C) was favorable for high gas and hydrogen yields. Char gasification improved from 27 to 13 wt. % and hydrogen yield increased from 36.2 to 49.2 vol. % with increase in steam/MBM (wt/ wt), while with increased in packed bed height increased gas (29.5 to 31.6 wt. %) and hydrogen (45 to 49.2 vol. %) yields. It didn’t show substantial effect on heavier hydrocarbons.

The kinetic parameters for the pyrolysis of meat and bone meal were determined using thermogravimetric analysis (TGA) at three different heating rates (10, 15 and 25 °C/min) using distributed activation energy model (DAEM). The activation energy was found in the range of 60-246 kJ/mol for the temperature range of 496-758 K and their corresponding frequency factors were 6.63 x 103 to 8.7 x 1014 s-1.