City Peak Shaving StationWhat is it like? Let's learn about it.

The city peak shaving station mainly includes systems for natural gas purification, liquefaction, storage, and vaporization. It consists of natural gas desulfurization units, dehydration units, mercury removal units, liquefaction units, LNG storage tanks, LNG export pumps, vaporization furnaces, BOG compressors, flares, metering skids, and loading skids.

Below is an introduction to the working process of the city peak shaving station:

Desulfurization

　　City Peak Shaving StationThe raw gas desulfurization process mainly removes acidic gases such as CO2 and H2S from the raw gas. The desulfurization gas uses a dual-tower process and chemical absorption method (alcohol amine method), with the solvent being N-methyl diethanolamine (MDEA) formulated solvent, using a 45 /-5wt% aqueous solution. The gas and methanol removal indicators are: CO2 content not exceeding 50ppm-mol, H2S content not exceeding 5mg/Nm3, mercaptan content not exceeding 3mg/Nm3, and total sulfur content not exceeding 30mg/Nm3.

Dehydration Unit

To prevent the water in the raw natural gas from freezing and blocking the liquefaction unit, the city peak shaving station removes water from the natural gas, and the water content in dehydrated natural gas should not exceed 1ppmv. The dehydration uses physical adsorption, with the drying agent being 4A molecular sieve.

Mercury Removal Unit

To prevent trace mercury in the raw gas from corroding equipment such as cold boxes at low temperatures, the city peak shaving station removes mercury through chemical adsorption, with the adsorbent being activated alumina or sulfur-loaded activated carbon. The natural gas from the dehydration unit enters the mercury removal tower, where the mercury content is reduced to below 10ng/Nm3 through the adsorption of the adsorbent.

Liquefaction System

The purified natural gas from the city peak shaving station enters the LNG plate-fin heat exchanger, where it is pre-cooled, and benzene and heavy hydrocarbons are removed from the natural gas. The light components, after the removal of benzene and heavy hydrocarbons, return to the LNG plate-fin heat exchanger, and the liquid at -155 flows out from the bottom of the LNG plate-fin heat exchanger, entering the LNG storage tank as LNG product after throttling.

LNG Storage Tank

　　City Peak Shaving StationThe LNG from the liquefaction unit enters the LNG storage tank at -160 and 0.01MPaG pressure. The pressure in the tank is controlled by compressing and recovering the evaporated gas generated in the tank through the BOG compressor. The BOG (approximately -160) from the LNG storage tank directly enters the BOG compressor for compression and export.

LNG Export Pump

Each LNG storage tank at the city peak shaving station is equipped with an export pump, which pressurizes the LNG in the tank to the vaporization unit for export or loading of LNG.

BOG Treatment Unit

The evaporation at the city peak shaving station is mainly caused by the input of external energy, such as the operation of pumps, external heat input, atmospheric pressure changes, environmental impacts, and the volume changes of evaporated gas in the tank when LNG is delivered into the tank. The purpose of the BOG treatment unit is to economically and effectively utilize the evaporated gas generated by the city peak shaving station, with the BOG treatment process being direct compression for external export.

Vaporization Export Unit

The pressurized LNG from the LNG export pump enters the vaporization furnace, where it is heated to normal temperature before entering the natural gas export pipeline.

Natural Gas Booster

Natural gas from the boundary area is boosted, filtered, and metered before entering the purification liquefaction unit.

Flare System

The flare system includes hot and cold flare pipelines, where the hot flare pipeline is used to collect hot waste gas from the liquefaction unit and booster system, while the cold flare pipeline is mainly used to collect overpressure discharges from the BOG main pipeline, discharges from the safety valve of the BOG compressor, and some discharge gases from the liquefaction unit.