Solvent injection for solids prevention in an LNG plant
A solvent is dispersed into a natural gas feed at a solvent injection point to produce a mixed feed. The mixed feed contains heavy components with a potentially fouling portion that can cause obstructions in a heat exchanger. A fluid injection system can inject the solvent intermittently, for instance, based on an amount of accumulation or expected accumulation of heavy component solids in the heat exchanger. The solvent prevents the potentially fouling portion of the heavy components from freezing, melts or dissolves the accumulation, and reduces the obstructions in the heat exchanger. The fluid injection system includes a solvent supply, an optional atomizer, an injection controller, optionally one or more sensors, and/or optionally a heater. The solvent injection system can disperse the solvent onto a flow surface for the natural gas feed and/or mixed feed to form a solvent film which further reduces heavy component solids.
1 . A method for reducing hydrocarbon fouling, the method comprising:
injecting a solvent into a feed of natural gas at a solvent injection point, the feed containing heavy components, the solvent injection point positioned upstream from a feed chiller heat exchanger, wherein injecting the solvent into the feed of natural gas includes directing the solvent onto a flow surface that conveys the feed of natural gas to form a solvent film on the flow surface upstream from the feed chiller heat exchanger;
producing a mixed feed from a dispersal of the solvent into the feed of natural gas, the mixed feed containing the heavy components;
directing the mixed feed into the feed chiller heat exchanger; and
preventing the heavy components of the mixed feed from freezing into a fouling portion in the feed chiller heat exchanger using the solvent including the solvent film formed on the flow surface.
2 . The method of claim 1 , wherein the mixed feed includes between one and 10000 parts per million by weight of the solvent.
3 . The method of claim 1 , wherein the solvent includes one or more of isoparaffins, isoolefins, isobutane, isooctane, isodecane, isododecane, isotetradecane, isohexadecane, diisobutylene, tri-isobutylene, tetraisobutylene, petroleum naphtha, kerosene, or cold weather diesel.
4 . The method of claim 1 , wherein the solvent includes an isoparaffin with a freezing point between −65° C. and −75° C.
5 . The method of claim 1 , wherein the mixed feed is a first mixed feed, the method further comprising:
outputting, from the feed chiller heat exchanger, a second mixed feed including the fouling portion of the heavy components.
6 . The method of claim 5 , wherein a concentration of the solvent in the second mixed feed prevents the fouling portion of the heavy components from freezing downstream of the feed chiller heat exchanger.
7 . The method of claim 1 , wherein the feed chiller heat exchanger is a propane feed chiller or an ethylene feed chiller of a cascading liquid natural gas (LNG) system.
8 . The method of claim 1 , wherein the solvent is a first solvent, the solvent injection point is a first solvent injection point, and further comprising injecting a second solvent into the feed of natural gas at a second solvent injection point, the second solvent being a different solvent than the first solvent.
9 . The method of claim 1 , wherein injecting the solvent into the feed of natural gas includes a plurality of intermittent injections of the solvent at the solvent injection point, and the method further includes determining an amount of an accumulation of solids in the feed chiller heat exchanger, a timing of the plurality of intermittent injections is based at least partly on the amount of the accumulation of solids.
10 . A method for reducing hydrocarbon fouling, the method comprising:
injecting a solvent into a feed of natural gas at a solvent injection point, the feed containing heavy components, the solvent injection point positioned upstream from a heat exchanger, chiller, debutanizer, or condenser, wherein injecting the solvent into the feed of natural gas includes injecting the solvent onto a flow surface that conveys the feed of natural gas to form a solvent film on the flow surface upstream from the feed chiller heat exchanger;
producing a mixed feed from a dispersal of the solvent into the feed of natural gas, the mixed feed containing the heavy components;
directing the mixed feed into the feed of the heat exchanger, the chiller, the debutanizer, or the condenser downstream from the solvent injection point; and
preventing, using the solvent including the solvent film formed on the flow surface, the heavy components of the mixed feed from freezing into a fouling portion in the heat exchanger, the chiller, the debutanizer, or the condenser.
11 . The method of claim 10 , further comprising:
melting, with the mixed feed, an accumulation of solids in the heat exchanger, the chiller, the debutanizer, or the condenser.
12 . The method of claim 11 , wherein the heat exchanger, the chiller, the debutanizer, or the condenser is in an operating mode during the melting of the accumulation of solids.
13 . The method of claim 10 , wherein a boiling point of the solvent corresponds to a boiling point of C7 to C13 hydrocarbons.
14 . The method of claim 10 , wherein the dispersal of the solvent into the feed of natural gas includes dispersing the solvent into the feed of natural gas with an open port for injection or an injection nozzle.
15 . The method of claim 10 , wherein the dispersal of the solvent into the feed of natural gas includes a liquid atomization process that disperses the solvent as droplets into the feed of natural gas.
16 . The method of claim 15 , wherein the liquid atomization process includes increasing a pressure or a temperature of the solvent prior to adding the solvent into the feed of natural gas.
17 . The method of claim 10 , further comprising removing the solvent and the heavy components using a heavies removal unit (HRU) downstream from the heat exchanger, the chiller, the debutanizer, or the condenser.
18 . A system for reducing hydrocarbon fouling, the system comprising:
an injection system injecting a solvent into a feed of natural gas containing heavy components at a solvent injection point, the solvent injection point positioned upstream from a feed chiller heat exchanger, wherein injecting the solvent into the feed of natural gas includes injecting the solvent onto a flow surface that conveys the feed of natural gas to form a solvent film on the flow surface upstream from the feed chiller heat exchanger; and
a mixed feed produced from a dispersal of the solvent including the solvent film formed on the flow surface into the feed of natural gas, the mixed feed containing the natural gas and the heavy components.
19 . The system of claim 18 , further comprising a controller controlling a flow of the feed of natural gas based on sensor data including solvent dispersal characteristics.