Davidyson - my apologies for the delay in replying to your questions. Until recently I'd resisted using e-mail and the internet, so info gathered over the years is on paper. I've had an interesting time seeing what's available on the web so that you can review it if you wish.
The scale and degree of modularity of construction will define the time taken "to build methanol conversion plants." Scale is a function of the costs of fuelwood transport, which appears to be best below about 3 miles. This gives a theoretical maximum area of about 28 sq mls which equals about 7,000 hectares. (For anyone who needs to know it, a hectare = 2.47 acres).
I've seen yields of >10 Tonnes Dry Wood/ha/yr in Venezuela, 5TDWd/ha/yr in UK, and 1TDWd/ha/yr in Norway. Taking 5TDWd/ha/yr as the yield, 7,000 ha.s would provide 35,000 TDWd/yr or around 100 Ts/day. For a plant this size, given a large degree of factory production of plant modules, I'd expect an on-site assembly period of less than six months.
It should be noted both that far larger unsustainable plants have been operating to provide methanol as a chemical feedstock, (for instance at Goole, UK, importing 70,000Ts /yr of Baltic conifer forest) and that smaller plants drawing on less than 7,000 ha.s will have lower transport costs. Also, in the interests of decentralization the smaller the operation can be (without untenable capital costs/ tonne output) the better.
The material conversion efficiency in the '80 was 1.0T methanol from 2.3TsDWd, or about 44%. It has since risen to about 55% and, following EU-funded research into reforming the tars & condensates produced during the wood's gasification is set to rise considerably further.
In terms of the energy efficiency of this conversion, dry deciduous wood is generally taken to have a potential of around 4,850 KWHrs/tonne. (For those who need to know, a tonne = 2,205lbs). Both the wood's gasification and the woodgas's conversion to methanol emit heat, a proportion of which is used in processing, with the remainder either being vented or put to use for a steam-turbine genny or possibly community heating. It is not accounted below.
On the present material conversion efficiency of 55%, a tonne of wood yields 550 kg Methanol = 2,994 KWHrs (methanol = 19.6MJ/kg). This gives an energy conversion efficiency of 61.7%. (The bonding in of an atom of Oxygen in the woodgas to make methanol CH3OH is part of the reason for the rise from mce:55%).
I'm loth to attempt your last question without a clear idea of what you mean by 'the world's current fuel demand' but would calculate the following.
Petrol= 44.5MJ/kg x 20% effic IC engine vehicle = 8.9MJ delivered
Methanol= 19.6MJ/kg x 44% effic FC vehicle = 8.62MJ delivered.
On these numbers we need 1.03Ts methanol to replace 1.0T petrol.
Therefore, per million tonnes of petrol replaced we'd need 1.03MT methanol which, at good UK growth rates, needs about 375,000 ha.s of land.
It is perhaps worth noting that even the tiny UK has over 10 million ha.s of deforested moorland and marginal hill pasture, much of which is producing less than 25 servings of lamb per year, largely at the taxpayer's expense. Given reasonable incentives, there are many areas where hill-farmers could be willing to reforest parts of their land with native deciduous species to supply feedstock to a local processing plant.
Below are some of the better web sites on the issue. None I'm afraid give a clear overall picture of the option from forestry to vehicle but each has relevant items that are worth hunting out.
Hoping I've written the addresses properly,