液化天然气供气站的工艺设计

TECHNICAL PROCESS DESIGN OF LNG DELIVERING STATION

LNG供气站的设计核心是工艺设计,设计中应注意以下几点:正确处理技术先进性与经济合理性的关系,综合权衡设置费与运营费的比例,力求项目全寿命费用最低;大多数城市LNG供气站均利用空气气化LNG,单罐容积为100m3的真空压力式储罐广泛用于储存量为1200m3以下的LNG供气站;为正确设置储罐安全阀的开启压力和排放压力,必须根据储罐的最高工作压力按照规范正确确定储罐的设计压力;储罐上2套独立的液位计和高、低限报警自动切断装置可确保储罐安全运行;空温式气化器的气化能力按用气城市高峰小时计算流量的1.3～1.5倍确定,为便于自然化霜应设置2套空温式气化器切换使用;空温式气化器出口串接水浴式加热器可提高冬季或雨天出口天然气温度,保护碳钢管道并降低供销差;LNG储罐区应设置围堰,消防用水量为喷淋与水枪用水量之和。最后建议,必须尽快颁布国家LNG设计规范,以提高我国的LNG设计水平。

For the southeast littoral where there is developed economy, but is far away from the trunk pipeline of gas transmission, LNG delivering is the main way to utilize natural gas. The key of LNG delivering station design is the technical process design. The following points should be considered in the design: the relationship between the advanced technology and the reasonable economy should be treated properly; the proportion of facility cost vs. operation cost should be weighted comprehensively to make the expense during the whole project life lowest; as for the most of urban LNG delivering stations where air is used to gasify LNG, the sub-atmospheric pressure tanks (100 m3/tank) should be used in the LNG delivering stations whose storage capacity is no more than 1200 m3; to set the cracking pressure and the discharge pressure of the safety valves correctly, the design pressure of tanks should be determined by the specification according to the maximum working pressure; the 2 sets of independent liquid level indicators and devices for high/low limit alarms and automatic cut-off should be installed to guarantee safe operation of the tanks; the gasification capacity of the air temperature gasifier should be determined by the 1.3~1.5 times of the peak gas delivering flow rate; 2 sets of the air temperature gasifiers should be installed for switching use to thaw frost naturally; the outlets of the air temperature gasifiers should be jointed with the water bath heaters to increase the temperature of the gas outlets in winter or raining days, protect the carbon steel pipes and reduce the volume difference between the gas delivering and selling; the cofferdam should be set up in the tank area and the water capacity for fire fighting should be the amount of sprinkle and water-gun consumption. At last, it is suggested the national specifications of LNG design should be issued as early as possible to improve the LNG design level in China.