# Process of Formaldehyde and Volatile Organic Compounds' Removal from Waste Gases
## 5 Co-Incineration of Waste Industrial Gases  
The waste gas treatment process described in Figure 1 is in accordance with existing EU directives and sufficiently reduces the concentration of formaldehyde in waste gases to comply with current standards, but it still releases about 280 kg of formaldehyde per year. By purifying the waste gases with water absorption, as shown in Figure 4, formaldehyde emission is reduced from 0.033 kg/h to about 0.0056 kg/h; about 0.027 kg/h formaldehyde is absorbed in water, which is then used as process water. In order to completely remove formaldehyde from waste gases, which contain other combustible organic substances, co-incineration with natural gas is recommended, with the resulting energy used to generate electricity. Proposed new technological process for off-gases' co-incineration from the metal oxide catalyst formaldehyde production processes reduces the levels of formaldehyde, carbon monoxide (CO), and volatile organic compounds (VOCs) to practically zero. The co-incineration process would use the combined-cycle gas turbine (CCGT) power system shown in Figure 5.  
Figure 5: Computer simulation of the co-incineration of waste industrial gases from metal oxide catalyst formaldehyde production processes in a combined-cycle gas turbine (CCGT). A combined-cycle gas turbine power system consists of the following components: Gas turbine, steam turbine, waste heat recovery units for steam generation, condenser, and other auxiliary equipment [22]. A combined-cycle gas turbine power system typically uses a gas turbine to drive an electrical generator and recovers waste heat from the turbine exhaust gas to generate steam, which drives a steam turbine to provide supplemental electricity. The overall electrical efficiency of a combined-cycle gas turbine power system is typically in the range of 50-60% [23]. Figure 5 shows the co-combustion of waste gases in the metal oxide catalytic formaldehyde production process; the waste gases (OFF-GAS) are mixed with air (AIR-IN) in a static mixer (MIX) before going into the compressor (COMP). The lower explosion limit of the carbon monoxide/air mixture is 12.5 vol.%, so no explosion will occur when compressing a very diluted off-gas/air mixture in the gas turbine compressor. The gas turbine is comprised of a compressor (COMP), a combustion chamber (COMBUST), which supplies natural gas (NAT-GAS) to the burners, and a turbine (TURB) that drives the generator. The gas turbine emits flue gases into heat recovery units for steam generation (ST-GENER), and the steam then goes into the steam turbine (ST-TURB) to provide supplemental electricity. The results of the computer simulation co-incineration of waste gases from formaldehyde production processes in combined cycle gas turbines (Figure 5) are given in Table 4, showing that the concentration of formaldehyde CO and VOC in the waste gases decreased practically to zero. The theoretical net power (Figure 5) of co-incineration of waste industrial gases from metal oxide catalyst formaldehyde production processes in a combined-cycle gas turbine is 4239 kW. According to the low heat value (LHV) of the natural gas, at the gas consumption of 577.5 kg/h the efficiency is 52.6%. To compare how much less natural gas is consumed to produce the same amount of electricity as in the process shown in Figure 5, a computer simulation of combined cycle gas turbines (CCGT) is shown in Figure 6 for electricity production using only natural gas. The results of the computer simulation of combined cycle gas turbines (Figure 6) are given in Table 5.  
According to the data of the waste off-gases' composition from the existing metal oxide catalyst formaldehyde production processes given in Table 1, the device for co-incineration of waste industrial gases with a combined-cycle gas turbine is small. This makes it difficult to optimize its performance in terms of maximizing efficiency. Newer, large CCGTs can achieve efficiencies of more than 55%, some even close to 60% [23].