Gas control layer

This section describes the elements in a closure or cap system of a completed landfill, including flexible membrane caps (FMCs), SWCR systems, gas control layers, biotic barriers, and vegetative top covers. It also discusses infiltration, erosion control, and long-term aesthetic concerns associated with securing a completed landfill. 

Figure 26.31 shows a typical landfill profile designed to meet U.S. EPA s MTG requirements.38 The upper subprofile comprises the cap, or cover, and includes the required 2-ft vegetative top cover, 1-ft lateral drainage layer, and low-permeability cap of barrier soil (clay), which must be more than 2 ft thick. This three-tier system also includes an optional FMC and an optional gas control layer. The guidance requires a 40-mil thick FMC. 

Gas control layer/system-gas control Filter layer—control the movement of particles... 

Control layers, such as those used to minimize animal intrusion, promote drainage, and control and collect landfill gas, are often included for conventional cover systems and may also be incorporated into ET cover system designs. For example, a proposed monolithic ET cover at Sandia National Laboratories in New Mexico will have a biointrusion fence with 1/4-in. squares between the topsoil layer and the native soil layer to prevent animals from creating preferential pathways, potentially resulting in percolation. The biointrusion layer, however, will not inhibit root growth to allow for transpiration. At another site, Monticello Uranium Mill Tailings Site in Utah, a capillary barrier ET design has a 12-in. soil/rock admixture as an animal intrusion layer located 44 in. below the surface, directly above the capillary barrier layer. 

Figure 26.32 illustrates two moisture control options in gas-collector systems. Gas-collector systems will tolerate a large amount of moisture before air transmissivity is affected. Condensates from the gas-collector layer that form beneath the clay and FMC can also be taken back into the waste, since most hazardous wastes are deposited very dry. 

Rella R., Rizzo A., Licciulli A., Siciliano P., Troisi L., Valli L., Tests in controlled atmosphere on new oprical gas sensing layers based on Ti02/metal-phtalocyanines hybrid system, Materials Science and Engineering C 2002 22 439-443. 

It was found that Sylgard 184 provided a higher tensile strength and elongation than RTV 615, and so the former was selected for fabrication of the microvalve control layer [449]. Moreover, the control channel must be filled with water before use, in order to prevent bubble formation in the fluidic channel due to the gas permeability of PDMS [449]. 

Membrane electrode assemblies (MEAs) are typically five-layer structures, as shown in Figure 10.1. The membrane is located in the center of the assembly and is sandwiched by two catalyst layers. The membrane thickness can be from 25 to 50 pm and, as mentioned in Chapter 10, made of perfluorosulfonic acid (Figure 11.3). The catalyst-coated membranes are platinum on a carbon matrix that is approximately 0.4 mg of platinum per square centimeter the catalyst layer can be as thick as 25 pm [12], The carbon/graphite gas diffusion layers are around 300 pm. Opportunities exist for chemists to improve the design of the gas diffusion layer (GDF) as well as the membrane materials. The gas diffusion layer s ability to control its hydrophobic and hydrophilic characteristics is controlled by chemically treating the material. Typically, these GDFs are made by paper processing techniques [12],... 

Fabricate highly controlled gas diffusion layers through fine gradient machine coating methods exploit a new structure-function approach to designing improved catalysts and catalyst alloys... 

In addition, the efficiency of electric contact between bipolar plates and gas diffusion layers was measured using special test station comprising a hydraulic press with a temperature control, current supply and control systems. The purpose of provided measurements is the comparative analysis of parameters of different bipolar plates and gas diffusion layers, and also obtaining of the necessary data for use in calculations on mathematical model. Resistance tests of gas diffusion layers and bipolar plates were performed both in a longitudinal direction (four-contact method) and in a transverse direction. 

In such cases, the synthesis gas reactor is then equipped with an increased number of quench gas controllers in order to maintain the higher temperature rise in the individual catalyst layers to be expected due to the weaker dilution in limits. The pressure drop across the overall loop is 6 10bar. The largest plants in operation have methanol reactors with an individual capacity up to 2500tpd. Since 1976, a plant with a capacity of 50tpd has been in operation in South Africa which is fed with synthesis gas from a coal gasification unit operating to the Koppers process. 

We have also used the STR PEM fuel cell to better understand the mass transport controlled regime of fuel cell operation. It is well known that the current or power output from a PEM fuel cell is reduced when air is used at the cathode instead of oxygen. Two effects can contribute to diminished fuel cell performance either the thermodynamic potential is reduced or the oxygen transport across the gas diffusion layer is reduced because of the presence of an inert gas. Figure 3.15 shows a series of I-V curves taken in the STR PEM... 

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