Can anybody tell me about LNG tankers and fuel consumption, do they burn boil off gas, HFO, MDO and how much?

Answer 1

The following is from Wikipedia:

Propulsion
LNG carriers are unique in that the large majority of them are propelled by steam turbines, with new ships still being built with this propulsion method. This is because the simplest way of handling the boil off gas (BOG) is to burn it in the ships' boilers, creating enough steam to propel the ship when supplemented with additional gas from the cargo tanks.

Diesel engines have largely replaced steam turbines in all other ship types, but until recently diesel engines adapted to run on BOG have not been widely utilised, even though the technology has been around since the early 1980's. However, the rapid expansion of the LNG fleet has meant that in the first decade of the 21st century there is a shortage of sea going personnel qualified to operate steam turbine ships. High prices for LNG are also driving the quest to maximise the yield from the transported cargo. Modified diesel engines burn less gas than steam turbines due to greater fuel efficiency. Combined cycle systems have also been implemented, with COGAS (COmbined Gas And Steam) electric propulsion arrangements having thermal efficiencies close to or greater than diesel engine systems. In this arrangement, the gas is burnt in a gas turbine and the waste heat from the gas turbine used to generate steam to run a supplementary steam turbine. However, recent developments have enabled the boil off gas to be re-liquified and returned to the cargo tanks, allowing conventional diesel engine propulsion systems to be utilised. All this has meant that coming into the 21st century the last refuge for steam ships could eventually disappear.

and the following is from CRYOSTAR Corp., a major supplier of Storage, Drive and Reclamation facilities for LNG Tankers:

LNG Tanker & Carrier equipment

Natural gas is conventionally transported over long distances in liquefied state. For example, ocean going LNG Tankers & Carriers transport liquefied natural gas from a first location, in which the natural gas is liquefied, to a second location in which it is vaporized and sent to a gas distribution system.

Since natural gas liquefies at cryogenic temperatures, i.e. temperatures well below -100°C, there is always a continuous boil-off of the liquefied natural gas during transportation. Accordingly, equipment needs to be provided in order to handle this boil-off.

Cryostar is the only supplier for the combined cryogenic machinery for the Cargo Handling System on LNG Carriers, i.e :
Boil-off Gas Compressors,
Gas Heaters and Vaporizers, as well as
Re-liquefaction Machinery and Reliquefaction Systems.

Irrespective of the selected ship drive system (conventional steam turbine, dual fuel engine, Diesel-electric drive system, gas turbine or Diesel engine with re-liquefaction plant), Cryostar has the right products for assuring the reliable operation of the ships' cryogenic systems.

Sophisticated Cargo Handling Equipment is used during loading and unloading of LNG to maintain optimum tank operating parameters, as well as for preparing the ship for operation, and during de-commissioning prior to dry-docking.

Cryostar's Product Matrix' allows easy selection for each ship drive system of the appropriate configuration of the Cargo Handling Machinery and Equipment.

The unique know-how among several disciplines of the cryogenics industry is the result of continuing efforts over the last 30 years for excellence in achieving specific, advantageous technical solutions, outstanding customer service and the best possible quality for critical equipment.

As a result, 2 out of 3 LNG Carriers have our equipment aboard, accounting for more than 13'000 successful voyages.

As you can see, there are many types of drives and storage, reclamation systems available and used so it is difficult to answer your question specifically.