An indirect evaporative cooling apparatus includes a housing, a heat exchanger core, a bypass valve, a filter, an indoor fan, and an outdoor fan. The heat exchanger core is in the housing. A first space, a second space, a third space, and a fourth space are formed by the heat exchanger core and the housing, and a first air vent, a second air vent, a third air vent, and a fourth air vent are disposed in the housing. The first space and the second space are connected by using the heat exchanger core to constitute an indoor circulation air duct, the third space and the fourth space are connected by using the heat exchanger core to constitute an outdoor circulation air duct.

A natural gas processing system is mounted on a mobile platform that is transported to a natural gas source, such as a well. The system supplies natural gas through multiple hose reels to operate multi-fuel engines for well field equipment such as pumps, compressors, and trucks. A coalescing filter removes contaminants from the natural gas. A generator powered by the natural gas supplies process electricity. A process control monitors and controls the natural gas processing system, including pressure, temperature, moisture, and flow sensors. A gas chromatograph will determine the chemical composition of the natural gas. A gas evacuation system removes gas from the hose reel assemblies in the event of an emergency. An emergency shutdown system will halt the process in the event of high liquid levels, a gas leak, fire, or gas composition out of specification.

An absorption filter structure with increased filter efficiency in an easily detachable form for optional use with a helmet structure. The absorption filter structure includes a filtration unit to pass external air through an internal space in a filtration direction. An absorption layer, a filtering layer and a shielding layer are stacked in the filtration unit. For filtering the external air, an external air vent, and an internal air vent are also provided. When combined with a helmet, the absorption filter structure is configured to be easily detachable from the helmet.