In this study, mono-digestion of rendering wastes and co-digestion of rendering wastes with potato pulp were studied for the first time in continuous stirred tank reactor (CSTR) experiments at 55 °C. Rendering wastes have high protein and lipid contents and are considered good substrates for methane production. However, accumulation of digestion intermediate products viz., volatile fatty acids (VFAs), long chain fatty acids (LCFAs) and ammonia nitrogen (NH4-N and/or free NH3) can cause process imbalance during the digestion. Mono-digestion of rendering wastes at an organic loading rate (OLR) of 1.5 kg volatile solids (VS)/m3 d and hydraulic retention time (HRT) of 50 d was unstable and resulted in methane yields of 450 dm3/kg VSfed. On the other hand, co-digestion of rendering wastes with potato pulp (60% wet weight, WW) at the same OLR and HRT improved the process stability and increased methane yields (500–680 dm3/kg VSfed). Thus, it can be concluded that co-digestion of rendering wastes with potato pulp could improve the process stability and methane yields from these difficult to treat industrial waste materials. 相似文献
The coupling effects of venting and CO2inerting on stoichiometric methane-air mixture explosions were investigated in an isolated vessel and interconnected vessels. The results indicate that venting mitigates the explosion intensity, especially for small vessels. For vessels connected by pipes, a venting design following EN 14994 (2007) and NFPA 68 (2013) could not meet the venting requirements. For an isolated big vessel and interconnected vessels, increasing the CO2 volume fraction (Φ) from 0 to 15.0 vol% decreased the maximum explosion overpressure (Pmax) and maximum rate of overpressure rise ((dP/dt)max) and delayed tmax. For closed interconnected vessels, Pmax varied approximately linearly with Φ. For both isolated vessel and interconnected vessels, the coupling effects of venting and CO2 inerting on methane-air explosion were more efficient than those of individual mitigative method (that is, venting alone or CO2 inerting alone). 相似文献
Runaway reactions are continuing to be a problem in the chemical industry. A recent study showed that 26% of our major chemical plant accidents are due to runaways. The consequences of runaway reactions are usually mitigated with (a) reliefs and containment systems or (b) shortstopping (reaction inhibition). This study covers the concept of shortstopping.
One of the major reasons for runaways is power failure. In the advent of a power failure, mixing an inhibiting agent with the reactor contents is challenging. However, jets or impellers driven by a small generator can be used for mixing. This study compares shortstopping results in vessels agitated with jets and impellers using computational fluid dynamics (CFD). A commercial CFD code, Fluent is used.
For shortstopping systems relying on jet mixing, angle and diameter of jet nozzle and jet velocity are the key design/operating parameters. For the systems with impellers, type, size and RPM of impeller are the key parameters. In this work, mixing with a jet mixer is first investigated for three nozzle diameters and two angles of injection. The best jet mixer configuration on the basis of mixing time is used for shortstopping studies. The simulated shortstopping results with the jet mixer are then compared with those obtained with impeller (Rushton and pitched blade turbine) stirred vessels. Our results identify the conditions for effective shortstopping; i.e., agitation requirements, locations for adding the inhibitor, and the quantity of inhibitor.
The distribution of excess inhibitor is shown to be an important and essential design criterion for effective shortstopping when using impeller stirred vessels. The comparative study with a single jet shows that jet mixer is ineffective when used for shortstopping. Efforts such as adding excess inhibitor and inhibition with higher reaction rates at the same power, proved to be ineffective when using jet mixer compared to the results with impellers. 相似文献
In the pulp and paper industry, lignin and other color compounds are removed by chemical agents in bleaching process. Use of chlorine-based agents results in production of degradation products which include various chloro-organic derivatives. Since these new compounds are highly chlorinated, they cause a problem in the treatment of pulp and paper industry wastewaters. Chemical precipitation, lagooning, activated sludge, and anaerobic treatment are the processes used for treating pulp and paper effluents. Furthermore, a combination of these processes is also applicable. In this study, the effluent of Dalaman SEKA Pulp and Paper Industry was examined for its toxic effects on anaerobic microorganisms by anaerobic toxicity assay. Additionally, this wastewater was applied to a sequential biotreatment process consisting of an upflow anaerobic sludge blanket as the anaerobic stage and a once-through completely mixed stirred tank as the aerobic stage. Results indicated that: (1) Dalaman SEKA Pulp and Paper Industry wastewater exerted no inhibitory effects on the anaerobic cultures under the studied conditions, and (2) application of a sequential biological (anaerobic/aerobic) system to treat the Dalaman SEKA Pulp and Paper Industry wastewater resulted in approximately 91% COD and 58% AOX removals at a HRT of 5 and 6.54 h for anaerobic and aerobic, respectively. 相似文献
To study the occurrence conditions and propagation characteristics of deflagration to detonation transition (DDT) in linked vessels, two typical linked vessels were investigated in this study. The DDT of the methane–air mixture under different pipe lengths and inner diameters was studied. Results showed that the CJ detonation pressure of the methane–air mixture was 1.86 MPa, and the CJ detonation velocity was 1987.4 m/s. Compared with a single pipe, the induced distance of DDT is relatively short in the linked vessels. With the increase in pipeline length, DDT is more likely to occur. Under the same pipe diameter, the DDT induction distance in the vessel–pipe–vessel structure is shorter than that in the vessel–pipe structure. With the increase in pipeline diameter, the length of the pipe required to form the DDT is reduced. For linked vessels in which detonation formed, four stages, namely, slow combustion, deflagration, deflagration to detonation, and stable detonation, occurred in the vessels. Moreover, for a pipe diameter of 60 mm and a length of 8 m, overdriven detonation occurred in the vessel–pipe–vessel structure. 相似文献