HEJ, HU ISSN 1418-7108 Manuscript no.: ENV-000624-A

The combustion parameters of gas mixtures

Although there are examples of the direct utilization of pure waste gases in the industry it is better justified to use it as combination gas on account of the fluctuation in its heating value and its availability.

A bio gas collector can be seen in Fig. 1. and the change of $CH_4$ is shown in Fig. 2 [1]. E.g. the fluctuation of heating value of coke gas and bio gas is shown in Fig. 3 and  4 [1] [2].

  

Figure 1: Bio gas collector

  

Figure 2: The fluctuation of $CH_4$ content of bio gas (Slovakia)

  

Figure: The fluctuation of heating value of coke gas (1999, DUNAFERR Co., Dunaújváros)

  

Figure 4: The fluctuation of heating value of bio gas (Bio gas plant, Slovakia)

It is most suitable to mix it with natural gas because this increases and stabilises thermal value and equalizes fluctuation of bio gas quality (Fig. 5).

  

Figure 5: Fluctuation of bio gas quality (Slovakia)

For our research project the basic calculations are done with a mixture of natural and waste gases.

For the calculations natural and waste gases having the main composition indicated in Fig. 6 were used. The Fig. 7 gives the values of the main combustion parameters which are most important from point of view of burners. In our calculations the ratio of waste gases varied between 0 and 60% in the gas mixture, taking the practice into consideration.

  

Figure 6: The main components of fuel gases

  

Figure 7: The change of heating value and density at different fuel gases

The same heat flow is guaranteed with increment of volume flow of fuel at different heating value of waste gases. For this reason the nozzle of burners applies transformation from time to time. The control of burners is necessary because of different density of waste gases . The theoretical combustion temperature plays a significant role in the heat technology and environmental protection. The bio gas has the minimum combustion temperature among the examined waste gases (Fig. 8) [3].

  

Figure 8: The change of theoretical combustion temperature of gas mixture

Mixing with natural gas rich in hydrogen the waste gases is favourable from the point of view of radiational heat transfer which is primarily important for heating furnaces and boilers. Coke gas increases the $H_{2}O$ content of flue gas, $CO_2$ content of flue gas will increase at bio gas - natural gas mixing and converter gas firing (Fig. 9).

In the formation of the mixture of waste gas and natural gas it is important to know the rate of flame propagation as well as flammability limits. As it is not an additive parameter, therefore the normal rate of flame propagation of gas mixtures cannot be calculated from the composition with the help of the mixture laws.

It can only be specified with the help of measurements [4]. Fig. 10 summarises the results of our measurements done to specify the exact values of flame propagation through example of coke gas [5].

  

Figure 9: $CO_2$ and $H_{2}O$ content in the flue gas

  

Figure 10: Flame propagation (v) of gas mixtures (natural gas-coke gas)

HEJ, HU ISSN 1418-7108 Manuscript no.: ENV-000624-A