This problem can be addressed as above by dilution with a lower viscosity solvent but with the same problems as above. Higher temperatures cannot be used as explained above also. The use of lower injector pressures will increase the problem of high viscosity, thus emphasising the need for system optimisation. This aspect is assigned a substantial part of the budget to allow for purchase of suitable expertise with design and test facilities in order to provide the most cost effective solution of unforeseen problems. As for the char problem, as application size increases, this problem reduces as more bio-oil is required to be injected per cycle.

4.4.3.3 Alkali metals

There is a small but finite amount of alkali metals in bio-oil from the wood ash. Some is in solution as, for example, acetates, while some is bound in with the char. Char removal will, therefore, contribute to reducing the alkali metal problem although there are problems with filtration as described above. It is not clear what will happen to these contaminants in applications. If used in an engine, they may deposit in the engine or be blown out. One possibility is that a suitable lubricant will flush any deposits into the sump where they can be dealt with during routine maintenance or by continuous in-line treatment. Turbines have more exacting requirements but required and achievable tolerances have not been determined.

4.4.3.4 ____ Inhomoaeneity of the bio-oil

Flash pyrolysis oils produced at low vapour residence times may suffer from a sort of phase separation when the lignin has not been fully depolymerised resulting in a sludge which can separate out with some char on prolonged storage. This problem becomes particularly acute in filtration of the oil when the pyrolytic lignin forms a sort of gel or jelly which rapidly and completely blocks the filter medium. It is possible that this problem can be mitigated or largely resolved by careful control separation, by homogenisation of the liquid or by the use of suitable additives.

4.4.3.5 ____ Environmental problems

One of the main justifications for the development of bioenergy applications is the positive contribution made to the environment. It is therefore important that the process operates in an environmentally acceptable way and that the environmental risks are minimised. Surprisingly little attention has been paid to any environmental aspect of biomass conversion either in terms of wastes and their management or disposal (12), or as an overall audit of the environmental implication or consequence of constructing such a system (13).